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A joint publication with TICCIH, 1996
Bridging rivers, gorges, narrows, straits, and valleys always has played an important role in the history of human settlement. Since ancient times, bridges have been the most visible testimony of the noble craft of engineers. A bridge can be defined in many ways, but Andrea Palladio, the great 16th century Italian architect and engineer, hit on the essence of bridge building when he said "...bridges should befit the spirit of the community by exhibiting commodiousness, firmness, and delight." In more practical terms, he went on to explain that the way to avoid having the bridge carried away by the violence of water was to make the bridge without fixing any posts in the water. Since the beginning of time, the goal of bridge builders has been to create as wide a span as possible which is commodious, firm, and occasionally delightful. Spanning greater distances is a distinct measure of engineering prowess.
In terms of engineering, bridges are discussed by design or type (beam, arch, truss, cantilever, suspension, or moveable); length (usually expressed in terms of clear or overall span); and materials (stone, wood, cast and wrought iron, and what we use today - concrete and steel). The purpose of this contextual essay is to provide parameters of value and significance so that we can focus our attention on those bridges - globally - that best illustrate the history of bridge building, and to encourage their preservation.
What is a World Heritage bridge? The World Heritage Committee states that to be of World Heritage status a monument or site must be of outstanding universal value. It must illustrate or interpret the heritage of the world in terms of engineering, technology, transportation, communication, industry, history, or culture. World Heritage industrial sites and monuments must meet one or more of the following criteria and pass the test of authenticity:
Represent a masterpiece of human creative genius;
Have exerted great influence, over a span of time or within a cultural area of the world, on developments in engineering theory, technology, construction, transportation, and communication;
Be an outstanding example of a type which illustrates a significant stage in bridge engineering or technological developments.
A World Heritage bridge, like other properties, must meet the test of authenticity in design, materials, workmanship, or setting (the Committee has stressed that reconstruction is only acceptable if carried out on the basis of complete and detailed documentation of the original artefact and to no extent on conjecture). The criteria of authenticity may apply to Japanese bridges like the Kintaikyo spanning the Nishiki River in Iwakuni or Palladio's bridge over the River Brenta at Bassano a Grappa near Venice (Italy). In the same context, some bridges have been moved when unable to function at their original location. It is not unusual in the USA, for example, to relocate a metal truss bridge to a less travelled road when it can no longer handle the traffic; the same probably holds true for other countries. This is within the functional tradition of some bridge types and should not be viewed as a negative factor in determining the integrity of a relocated structure.
The definition of authenticity is in the process of being expanded to include intangible values such as a bridge that embodies the spirit or character of a people or place, as New York City is embodied in the Brooklyn Bridge, San Francisco in the Golden Gate, London in Tower Bridge, Sydney (Australia) in the Harbour Bridge, or Bosnia-Herzegovina in the recently destroyed Stari Most in Mostar.
Bridges nominated for World Heritage listing also must have legal protection and management mechanisms to ensure their conservation. The existence of protective legislation at the national, provincial, or municipal level is therefore essential and must be clearly stated in the nomination. Guidelines for nominations state that each property should be compared with properties of the same type dating from the same period, both within and outside the nominating State Party's borders.
For the purpose of this contextual essay, bridge design and construction is dealt with chronologically by material and by type. In addition to the obvious evaluation factors as age, rarity, integrity, and the fame of the builder, consideration also is given to the substructure (piers, abutments, foundation), the superstructure (beam, arch, truss, suspension, and combinations thereof), the materials of construction (their strength and properties), the evolution of construction techniques, and whether the bridge advanced structural theory or methods of evaluating material behaviour.
Bridges discussed in this essay illustrate important types or technological turning points and are listed at the end. Some, like the Pont du Gard (France) and the Iron Bridge (UK), are already inscribed on the World Heritage List. Others may be candidates for listing given adequate study, comparison, and evaluation. Not every potential World Heritage bridge candidate is cited. It is the job of TICCIH and its member countries to identify and make a case for outstanding bridges so they can be appreciated and protected like the great architectural and natural monuments already designated.
The first bridges were natural, such as the huge rock arch that spans the Ardèche in France, or Natural Bridge in Virginia (USA). The first man-made bridges were tree trunks laid across streams in girder fashion, flat stones, such as the clapper bridges of Dartmoor in Devon (UK), or festoons of vegetation, twisted or braided and hung in suspension. These three types - beam, arch, and suspension - have been known and built since ancient times and are the origins from which engineers and builders derived various combinations such as the truss, cantilever, cable-stayed, tied-arch, and moveable spans.
The essential difference among types is the way they bear their own weight - the "dead load" and the "live load" - a person, the railway train, wind, or snow that is applied to the bridge. The weight of beam, truss, and girder bridges bears directly downwards from their ends on the ground, piers, or abutments. Arch bridges thrust outwards as well as downwards, acting in compression. The cables of suspension bridges act in tension, pulling inwards against their anchorages.
If two or more beam or girder spans are joined together over piers, they become continuous, a form favoured by European engineers, who had the mathematical knowledge to analyse the indeterminate stresses introduced by such systems. A case in point is the Town lattice truss invented by Ithiel Town, an American, in 1820, which is a rare instance of reverse techno- logical transfer. The form originated in the USA, but was widely adopted in Europe, especially in iron railway bridges. The lattice fell into disfavour in the USA, where a preference existed for statically determinate bridges of heavy timber, whose forces were easier to calculate.
A more complex form of the beam is the truss, a rigid self- supporting system of triangles transferring both dead and live loads to the abutments or piers. A more complex form of the girder is the cantilever, where trussed and anchored ends of the girder support a central span. They were favoured for deep gorges or wide fast-flowing streams where false work, a temporary structure, usually of timber, erected to assist in the construc- tion of the permanent bridge, is impossible to build. The three principal types - beam, arch, and suspension - often were combined in a variety of ways to form composite structures, the type selected depending on the nature of the crossing, the span required, the materials at hand, and the type of load anticipated - pedestrian, vehicular, railroad, or a channel of water as in aqueducts.
Other than the clapper bridges of England and similar spans surviving in other countries, bridges dating from prehistoric periods are rare. Bridges of twisted vines and creepers found in India, Africa, and South America, the ancient cantilevers of China, Kashmir, and Japan, if any survive, or the wooden arches of Japan may be candidates for World Heritage listing because they perpetuate primitive ingenuity and craft technology that is important to recognize. Since some of their materials cannot be original, these structures will have to pass the test of authenticity.
In 51 BC, during the Gallic War, Caesar attested to the construction of narrow wooden bridges by Gallic builders over wide rivers as the Loire, Seine, and Allier of 600ft (200m) span, used by pedestrians and domestic animals. The stone vault probably first sprang forth in Anatolia and the Aegean region of Asia Minor (central and western Turkey) in the 2nd millennium BC for short spans in civic construction. The Mesopotamian civilizations introduced the first major development of brick vaulting in the royal palaces, and also probably the first important arch bridges in the 6th century BC.
Figure 1 Ponte Saint-Martin (c 25 BC) near Torino (Italy). Shunsuke Baba, photographer
The greatest bridge builders of antiquity were the Romans. They applied a civil engineering repertoire on an unprecedented grand scale and achieved impressive results. Roman engineering introduced four significant developments to the art of bridge building that never had been prominent before: the discovery and extensive use of natural cement, development of the coffer dam, perfection and widespread application of the semi-circular masonry arch, and the concept of public works (Figure 1).
In these important respects, the Roman engineer vastly improved upon the efforts of his predecessors. Public water supply was the most significant aspect of Roman civil engineering: nothing like it had been achieved before nor was it to be emulated until the 19th century. Structural evolution achieved by Roman engineers is manifest in aqueducts, dam construction, and highway bridges that relied on the development of concrete, and a growing awareness of its strength.
The Romans mixed a cement, pozzolana, found near the Italian town of Pozzuoli (ancient Puteoli), with lime, sand, and water to form a mortar that did not disintegrate when exposed to water. It was used as a binder in piers and arch spandrels, and mass-formed in foundations. Coffer dams (temporary enclosures built in river beds to keep the water out while the foundations were established) were made by driving timber piles into the river bed, removing water from the area enclosed, and then excavating the soft ground inside. Despite the use of coffer dams, Roman bridge foundations typically were not deep enough to provide sufficient protection against scour. Most of the Roman bridges that survive are those built on solid rock such as the Pont du Gard aqueduct (c AD 14) near Nîmes (France), the Alcantara Bridge (AD 98) on the Spanish-Portuguese border, and the aqueduct at Segovia (AD 98), which are three of the most famous surviving Roman bridges and aqueducts. Scholars have researched Roman bridges and aqueducts for many years, so it should be possible to arrive at a well reasoned selection of Roman-built bridges for World Heritage listing.
Bridges of Asia
Figure 2 Phra Phutthos (12th century), Kompong Kdei vicinity (Cambodia), was constructed at the end of the 12th century during the reign of Jayavarman VII. With more than twenty narrow arches spanning 246ft (75m), this is the longest corbeled stone-arch bridge in the world. Institute of Asian Culture, Sophia University, Tokyo, Japan
Bridge building in Asia extends back earlier in time than in Europe. Because structural concepts of suspension, cantilever, and arch were first developed there with great sophistication, every effort should be made to identify surviving examples (Figure 2). China was the origin of many bridge forms: Marco Polo told of 12,000 bridges built of wood, stone, and iron near the ancient city of Kin-sai. The first chain-link suspension bridge, the Panhogiao or Panho Bridge (c206 BC), was built by General Panceng during the Han Dynasty. In 1665, a missionary named Kircher described another chain-link suspension bridge of 200ft (61m) made up of twenty iron links, a common bridge type built during the Ming Dynasty that was not adapted until the 19th century in America and Europe. China's oldest surviving bridge, and the world's oldest open-spandrel segmental arch, is the Zhaozhou Bridge (c AD 605), attributed to Li Chun and built south-west of Beijing in Hebei Province during the Song Dynasty. Its thin, curved stone slabs were joined with iron dovetails so that the arch could yield without collapsing. This technique allowed the bridge to adjust to the rise and fall of abutments bearing on spongy, plastic soils and the live loads of traffic.
Following the decline of the Roman Empire with its many engineer- ing achievements, beam, arch, suspension, and cantilever bridge building flourished in China while languishing in Europe for nearly eight centuries. Chinese bridge builders experimented with forms and materials, perfecting their techniques. Selected examples, found in the countryside and parks, may be candidates for World Heritage listing.
Other fine bridges survive in Iran, such as the Bridge of Khaju at Isfahan (1667), with eighteen pointed arches, carrying an 85ft (26m) wide roadway with walled, shaded passageways, flanked by pavilions and watch towers. This magnificent bridge, combining architecture and engineering in splendid functional harmony, also served as a dam, and included a hostelry where travellers found cool rooms for rest and refreshment after hot desert crossings (Figure 3).
Picturesque bridges, such as the Kintaikyo at Iwakuni (1673), with its five wooden arches intricately wedged, slotted, and dovetailed together, are found in Japan. The superstructure of this bridge has been rebuilt for centuries (the central three arches every 18- 22 years, and the side spans every 36 years), maintaining the fine craft tradition of the bridge keepers for centuries (Figure 4). Shogun's Bridge (1638), crossing the Daiya-gawa River in the sacred City of Nikko, is the oldest known cantilever. The bridge was badly damaged in the typhoon of 1902, rebuilt, and exists today bearing foot traffic. It consists of hewn stone piers pierced with rectangular holes that permit the insertion of tightly fitting cut-stone struts, two anchor spans, timber beams jutting out in cantilever form, and a suspended span.
Figure 3 Bridge of Khaju (1667), Isfahan (Iran), combining architecture and engineering in splendid harmony, functioned as a bridge, dam, and a resort for thirsty travellers coming off the desert.
Shunsuke Baba, photographer
Figure 4 Kintaiko (1673), Iwakuni (Japan), with its five wooden arches intricately wedged, slotted, and dovetailed, has been faithfully rebuilt for centuries. Each generation of craftsmen has carefully replicated the joinery techniques and materials of their predecessors.Shunsuke Baba, photographer
The revival of bridge building in Europe following the fall of the Roman Empire was marked by the spread of the pointed arch westward from its origins in the Middle East. The pointed arch typically was a Gothic architectural form important structurally in the development of palaces, castles, and especially the cathedrals of western Europe, but not very important for bridges. Medieval bridges continued such multi-functional traditions as the Isfahan Bridge in Iran. Chapels, shops, tollhouses, and towers adorned fortified bridges such the 1355 Pont Valentré at Cahors (France) or the Monnow Bridge (1272, 1296) at Monmouth, Wales (UK), which were built with defensive ramparts, firing slits, and drawspans.
Christian religious orders formed after the fall of the Roman Empire greatly assisted travellers by building bridges. In western and central Europe, religious groups managed popular financial institutions, with Papal sanction, both for bridge construction and for hospitals. The influence of these groups lasted from the end of the 12th to the early 14th century, and their perseverance ensured the construction of major bridges over wide rivers as the Rhône and the Danube.
The bridge over the Rhône at Avignon (1187), for example, a wooden deck on stone piers, was built by such an order under the inspired vision of a young shepherd, later canonized as St Bénézet for his accomplishment. The four surviving arches, dating from the bridge's rebuilding around 1350, rank as one of the most remarkable monuments of medieval times in view of the 101-110ft (31-34m) elliptical arches with radii varying at the crown and haunches.
As the Middle Ages drew to a close, stone arches of remarkable spans were built in mountain valleys where rock abutments provided solid foundations for spans in excess of 150ft (50m), such as the Vieille-Brioude and the Grand Pont du Doux in France.
Renaissance and Neo-Classical bridges
The great era of medieval bridge building was followed by the Quattrocento, the transition period from the medieval period to the Italian Renaissance, when the confidence and unbounded enterprise of engineers was manifested in bridges like the 1345 Ponte Vecchio, an early Florentine bridge in Italy, designed by Taddeo Gaddi, that carries a street of goldsmiths' shops on three segmental arches. This was followed by the technical efficiency and artistic advancement of Renaissance ideals of civic order during the Neo-Classical period of the 17th and 18th centuries, represented by long span and multiple stone arches: eg Santa Trinità (1569) in Florence, the Rialto (1591) in Venice, and the Pont Neuf (1607) in Paris. These bridges, which are among the most famous bridges in the world today, are all on the World Heritage List, although only as components of historic town centre inscriptions. Renaissance engineers had learned much about foundations since Roman times, though they rarely were able to excavate deeply enough to reach hard strata. They had, however, perfected techniques of spread footings - wide timber grillages resting on piles driven into the river bed upon which stone piers were laid. In the foundation of the Rialto Bridge, designer Antonio da Ponte drove six thousand timber piles, capped by three stepped grillages so that the abutment stones could be laid perpendicular to the thrust lines of the arch. Though built on soft alluvial soils, the bridge continues to support a street of jewellery shops enjoyed by tourists four centuries later.
The end of the Italian Renaissance witnessed a new vision of bridge construction. More than merely utilitarian, bridges were designed as elegant, grand passage-ways that were part of the visual perspective of the idealized cityscape - major accents to the totally redesigned merchant and capital cities. No country attempted to advance this concept more than France at the end of the 16th century, where a national transportation department of architects and engineers was set up, responsible for designing bridges and roads (Ponts et Chaussées). This corps of specialists gave the Neo-Classical period a range of monumental and elegant bridges on rivers as the Loire (Blois, Orléans, Saumur) and the Seine in Paris. This model spread all over Europe, producing large monumental urban bridges in capitals such as London, Saint Petersburg, and Prague.
In Italy, Bartolomeo Ammannati evolved a new form for the Santa Trinità Bridge - a peculiar double-curved arch whose departure from an ellipse was deliberately concealed by a decorative escutcheon at the crown. Its 1:7 rise-to-span ratio resulted in an elegantly shallow, long-arch span widely adapted in other bridges of the Renaissance. The bridge was reconstructed using original stones recovered from the river following demolition during World War II.
By the mid-18th century, masonry bridge building had reached its apogee. French engineer Jean-Rodolphe Perronet designed and built the Pont de Neuilly (1774), the Pont de Saint-Maxence (1785), and the Pont de la Concorde (1791), the latter completed when Perronet was eighty-three. Perronet's design goals were to slim down the piers and to stretch arches to the maximum. The Pont de la Concorde still represents the perfection of masonry arch construction, even though sceptical officials forced Perronet to shorten the unprecedented centre span of the bridge to 92ft (28m). Long, elegant, elliptical arches, piers half their former widths, special machinery for construction, and the introduction of an architectural motif used until the 1930s, the open parapet with turned balusters, completed this outstanding bridge. Widened in the 1950s, its original appearance was carefully maintained. Another masterpiece of the French Classical style is the Pont de Bordeaux of nineteen arches, more than 1640ft (500m), completed in 1822.
Figure 5 Pontypridd Bridge (1756) over the Taff in South Wales (UK), had to be rebuilt several times until its builder, William Edwards, got the correct rise-to-span ratio to ensure that the 140ft (43m) arch would not collapse after removal of the falsework.Shunsuke Baba, photographer
In the United Kingdom, a young Swiss engineer, Charles Labelye, was building the English equivalent of Perronet's bridges. On his first bridge, Westminster (1750) over the Thames, he developed the caisson, which made it possible for pier foundations to be built in deep, fast-flowing waters. To solve a problem that had confounded bridge builders since Roman times, Labelye used huge timber boxes constructed on shore, floated into position, and slowly sunk to the bottom of the river by the weight of the masonry piers being laid above. Fifteen semicircular arches, incrementally diminishing in length from the centre and rising in a graceful camber, set a high engineering and architectural standard that stood for over a hundred years.
England's other great bridge designer during this period, John Rennie, built the first Waterloo Bridge in 1811. Its level road and arches lasted until 1938. Rennie's next great bridge was Southwark Bridge (1819), also over the Thames in London, which was built not in stone but in the new miracle material of the 19th century - cast iron. It had three arches whose central span of 240ft (73m) dramatically demonstrated the potential of the new material.
Wooden bridges are some of the most ancient. The first Roman bridge, the Pons Sublicius (c 621 BC), was a wood-pile structure over the Tiber in Rome, extending pedestrian access to the Aventine Hill. The earliest detailed description of a wooden bridge, a timber-pile structure over the Rhine constructed in 55 BC, was written by Julius Caesar in his De Bello Gallico. The best extant model of this type survives today over the Brenta at Bassano a Grappa, near Venice. It was built by Palladio in 1561, destroyed in 1945, and reconstructed identical to the original in 1948.
By the mid-18th century, carpenters working in the forested regions of the world further developed the timber truss bridge. The most famous were two Swiss brothers, Johannes and Ulrich Grubenmann, who built bridges at Schaffhausen, Reichenau, and Wettingen that combined diagonal struts and trusses to produce remarkably long spans for their time. The Schaffhausen Bridge (1757), over the Rhine in northern Switzerland, had two spans, 171ft and 193ft (52m and 59m) respectively, which rested lightly on an intermediate pier when loaded. It was burned by the French in 1799 during the Napoleonic Wars. One of the few Grubenmann bridges to survive is Rumlangbrücke (1766), with a span of 89ft (27m).
Figure 6 Bridgeport Bridge (1862), clear-spanning 208ft (63m) over the South Fork of the Yuba River near Grass Valley, California (USA), has two parallel trusses based on the Howe patent of timber and iron rods, flanked by solid wooden arches cut to the curves and reflected in the exterior siding. It is the second longest covered wooden bridge span in the USA, after the Blenheim Bridge (1855) in New York State, which is 210ft (64m). Jet Lowe, HAER Collection
European engineers visiting the New World during the 19th century marvelled at the spans achieved by American timber bridges. Especially noteworthy was Louis Wernwag's 340ft (104m) arch truss of 1812, the "Colossus," over the Schuylkill in Philadelphia, the longest spanning bridge in the world at the time. Covered bridges, sheathed in wood to keep the structural timbers from deteriorating, are an icon of the American landscape. Outstanding spans that survive today include the Cornish-Windsor Bridge (1866) over the Connecticut River and the Bridgeport Bridge (1862), whose clear span of 208ft (63m) makes this gateway to the California goldfields the second longest single span. According to the National Society for the Preservation of Covered Bridges Inc, some 800 wooden covered bridges survive in the USA, more than in any other country (Figure 6).
Regardless of the capability of advanced societies like the Romans to build bridges in stone, the material for the ages, its cost always remained a problem. Wooden bridges were an economic alternative important to every civilization during all historic periods from prehistoric times to the first American settlement, from classical Rome to the European Enlightenment, including China, Japan, and south-east Asia. Wooden bridges have played a major role in the history of human development. The architectural varieties and structural types - girder, arch, suspension, truss, pontoon, and covered - were numerous. By virtue of the nature of their material, extant examples are scarce, as is the historic record. Nature, acts of God, war, and arson have decimated wooden bridges throughout time. A special global effort should be initiated to identify, access, and protect wooden structures of all kinds. A group of experts should be convened in the USA and in other parts of the world where timber bridges survive to recommend a selection for nomination to the World Heritage List.
Theoretical advances during the Renaissance and Neo-Classical period
Thanks to Galileo, Renaissance mathematicians and scientists understood beam action and the theory of framed structures. The truss, used by the Romans as stiffening on the Rhine bridge (55 BC) and in roof structures, was refined by the Italian architect- engineer Andrea Palladio. His classic treatise on Greek and Roman architecture, I Quattro Libri dell'Architettura, was published in 1570, and was widely distributed after translation into English by Isaac Ware in 1755. It contained the first drawings of a truss, the simplest and most easily visualized form for transferring both dead and live loads to piers and abutments, accomplished by a rigid self-supporting system of triangles. Palladio built several truss bridges, the most important being the Bassano Bridge (1561) over the River Brenta in the Veneto region in northern Italy. Destroyed several times, it has been carefully rebuilt faithfully following the original layout and exists today as the only example of one of Palladio's bridges.
The truss form, derived from the Romans, represents one of the Renaissance's most significant contributions to bridge building. Renaissance engineers also devised daring innovation in arch forms - the segmental, elliptical, and multi-centred.
The Hungarian, Janos Veranscics, reviewed these and other achievements in the structural arts at the end of the Renaissance in Machinae Novae, published in 1617. Several concepts that later became standard bridge practice first were illustrated in this volume: the tied arch, the Pauli or lenticular truss (in wood), the all-metal truss (in cast brass), a portable, metal chain-link suspension bridge, the use of metal in reinforcing wooden bridges, and the eye-bar tension member (again in brass).
In 1716, Henri Gautier published Traité des Ponts, the first treatise devoted entirely to bridge building, during the Age of Reason when empirical bridge design gave way to rationalism and scientific analysis. The book became a standard work of reference throughout the 18th century. It covered both timber and masonry bridges, their foundations, piers, and centring.
A far-sighted policy that led to the first national department of transportation in France was started by Henri IV and Sully at the end of the 16th century. During the second half of the 17th century, it was reorganized by Colbert as the Corps des Ingénieurs des Ponts et Chaussées, a group of state architects and engineers, during the reign of Louis XIV. In 1747, the École des Ponts et Chaussées, the oldest academic institution in the world for civil engineering education in the design of roads and bridges, was started, with Perronet as its first director. The first theoretical studies concerning the stability of arches, transmission of forces, and the multi-radius form were conducted at the school by La Hire, Gautier, Bélidor, Coulomb, and Méry.
Though extremely versatile, wood has one obvious disadvantage - it burns. Wernwag's Colossus, destroyed by fire in 1838, is but one example of many outstanding wooden bridges lost in this manner throughout history. There was another material, however, whose use at the end of the 18th century offered bridge engineers an alternative to the traditional materials of timber, stone, and brick. Although it had first been used in antiquity, iron was the miracle material of the Industrial Revolution. The Greeks and Romans had used it to reinforce stone pediments and columns in their temples and iron links had been forged by the Chinese and used in suspension bridges.
The successful smelting of iron with coke, rather than charcoal, by English ironmaster Abraham Darby in 1709 freed iron production from fuel shortage restrictions, made large castings possible, and facilitated creation of the arch ribs for the world's first iron bridge, built seventy years later. In 1754, Henry Cort of Southampton (England) built the first rolling mill, making possible the efficient shaping of bar iron; in 1784 he patented a puddling furnace by means of which the carbon content in cast iron could be reduced to produce malleable iron. These two milestones of metallurgy realized the potential of iron as a major building material. Bridges were one of the first structural uses of iron, preceded only by columns (not yet beams) to support the floors of textile mills.
Figure 7 Dunlaps Creek Bridge (1839), Brownsville, Pennsylvania (USA), spans 80ft (24m) on five elliptical ribs of cast iron made of nine 14ft (4m) segments flanged at the ends and bolted. The triangular bracing in the spandrels is reminiscent of Telford's iron bridges in Shropshire (UK), and the tubes resemble the eliptical arches of the Pont du Carrousel, built over the Seine in Paris in 1834. Library of Congress
The first successful all-iron bridge in the world was designed by Thomas Farnolls Pritchard, an architect who suggested using the material as early as 1773. Built by two ironmasters, Abraham Darby and John Wilkinson, to demonstrate the versatility of cast iron, the bridge spans 100ft (30m) over the River Severn at Coalbrookdale (UK), on five semi-circular ribs of cast iron. The Iron Bridge was followed by a succession of cast-iron arches built throughout Europe. Few cast-iron arch bridges were built in the USA as the iron truss, derived from wooden forms, was preferred. One iron arch, however, merits mention, as it is the oldest iron bridge in America. Dunlaps Creek Bridge (1839), designed by Captain Richard Delafield of the Army Corps of Engineers for the National Road in Brownsville, Pennsylvania, survives to this day, still carrying traffic (Figure 7). Because the material could be moulded into elaborate shapes, extravagantly decorative iron arches were used for pedestrian bridges on the grounds of estates and imperial palaces, such as Catherine the Great's Tsarskoye Selo in St Petersburg (Russia), or urban pleasure grounds, such as Central Park in New York City (USA). Both places have remarkable collections of cast-iron arch bridges.
Figure 8 Royal Albert Bridge, Saltash, Cornwall (UK), was the last great enterprise of Isambard Kingdom Brunel, England's foremost Victorian engineer. This photograph served as the frontispiece to William Humber's A Complete Treatise on Cast and Wrought Iron Bridge Construction, published in 1864, and shows one of the great lenticular spans being jacked into place. It was 445ft (135m) long, consisting of a single wrought-iron elliptical tube upper chord and a curved bottom chord of linked eyebar chains connected by open truss bracing. The trusses were fabricated on shore, then floated into position and jacked into position over the Tamar. Institution of Civil Engineers, London
Engineers in the 19th century improved the technology of sinking foundations to bedrock. Up until that time, coffer dams and crude caissons were the only means by which foundations could be constructed in water. Their use was limited by the length of wooden piles and by soils that were unsuitable for pile driving because they were either too soft or too hard. Credit for developing the first pneumatic caisson belongs to William Cubitt and John Wright, who used the technique on the bridge (1851) over the River Medway at Rochester (UK). It was similar to the caisson developed by Labelye, but differed in that the chamber resting on the river's bottom was airtight and required workmen to enter by means of airlocks after the water had been driven out by pneumatic pressure. Working in this environment, men suffered from the little understood "caissons disease," now better known as "the bends." The eventual diagnosis of this condition permitted the construction of bridges of unprecedented scale, overcoming the impediment of deep, broad rivers. Isambard Kingdom Brunel used the technique for sinking the piers of his bridge at Chepstow, Wales (UK) and, on a much grander scale, on the Royal Albert Bridge (1859) over the Tamar at Saltash in Cornwall (Figure 8). Here, the central pier was built on a wrought-iron caisson 37ft (11m) in diameter, sunk to bedrock in 70ft (21m) of water and 16ft (5m) of mud.
Another improvement in foundations in the early 19th century involved hydraulic cement. A better scientific understanding of the material by the Frenchman Vicat and the Englishman Aspdin and discovery of the material in a natural state in 1796 on the Isle of Sheppey in the Thames estuary, by Lafarge at Le Teil (France), and by Canvass White on the Erie Canal in New York in 1818, led to its use in sinking foundations by the new method of direct flow into coffer dams underwater, as at the suspension bridge at Tournon (France) in 1824. Hydraulic cement had the amazing ability to set under water, and was consequently used in aqueducts, piers and abutments, culverts, and locks.
Following the construction of the Iron Bridge at Coalbrookdale, Thomas Telford, a gifted, self-educated Scottish engineer, built a number of cast-iron arches throughout the British Isles. These included canal aqueducts, which were extraordinarily innovative arrangements in which the cast iron had real structural value. On both the Longdon-on-Tern (1796) and the Pontcysyllte (1805) aqueducts, the cast-iron sections that formed the side walls of the trunk were wedge-shaped, behaving like the voussoirs of a stone-arch bridge and bolted through flanges. Telford's most ambitious notion, however, was his proposal of 1800 for a single cast-iron arch of 600ft (183m) span over the Thames to replace Old London Bridge. An earlier proposal was unveiled in France by Montpetit in 1779 for a bridge of 400ft (122m) over the Seine, thought to have been the inspiration for Telford's idea. Even the young United States got into the act when Thomas Paine, the political philosopher, proposed an iron arch of 400ft span over the Schuylkill in Philadelphia. But the next most outstanding achievement after Coalbrookdale was the cast-iron arch over the River Wear at Sunderland (UK), because it actually was built. Completed in 1796 by Thomas Wilson, the bridge had an unprecedented span of 236ft (75m).
Figure 9 Rio Cobre Bridge (1800), Spanish Town, Jamaica, the oldest iron bridge in the western hemisphere, was designed by Thomas Wilson and employs the same iron voussoir, incremental circular spandrel bracing, and cast-iron plate deck as the earlier Wearmouth Bridge. Essentially a "kit bridge," the system of small castings held together by wrought-iron ties, tubes, and bolts lent itself to export. Many bridges of this type were shipped to distant colonies of the British Empire Eric DeLony, photographer
Today, several collections of cast-iron arches survive in different countries, the largest being in the United Kingdom, six in the USA, a few in France and Spain, and a remarkable selection surviving in Russia, dating back to the reign of Catherine the Great. These need to be studied and a selection made for nomination.
By 1800, most European engineers were open to using cast iron. Architects, however, preferred traditional materials such as granite and marble for the visible parts of buildings and wood for hidden structural parts like roof trusses, and did not accept cast iron as having aesthetic merit or structural value. In the USA, still blessed with abundant virgin forests, the early 19th century was the era of "carpenter engineers." Men like Timothy Palmer, Lewis Wernwag, Theodore Burr, and Ithiel Town followed British custom by conceiving and building truss forms predicated on intuition and pragmatic rules of thumb. Their craft tradition of knowledge, passed down from master to apprentice, contrasted with the scientific analysis and mathematical formulas practised by French government engineers. Models were built and loaded to failure and broken members replaced with stronger ones until the model supported loadings equivalent to a real live load plus a safety factor.
Patents were granted in the USA for composite wood and iron bridges, transitional structures that capitalized on the availability of cheap timber. When the American iron industry caught up with Europe's by the mid-19th century, bridge building took the direction of composite pin-connected trusses, with sophisticated castings for joint blocks and compression members, and forged eyebars and wrought-iron rods for tension members, all fabricated to high tolerances. This allowed them to be assembled easily and inexpensively in the field by unskilled labour using simple tools and erection techniques. The system prevailed in the USA because that country lacked a skilled labour force, and the remoteness of many bridge sites hampered the use of sophisticated machinery or the shipping of large bridge parts over long distances. A spirited debate ensued between England and the former colony during the last quarter of the 19th century over which system was best: easily erected pin-connected trusses on the "American plan," or European-style riveted trusses. Even though the rigid riveted truss was of superior design, American bridges remained competitive in world bridge markets until the early 20th century because they were cheaper and swiftly erected.
Figure 10 Gauntless Viaduct (1825) is the only fragment of the original Stockton & Darlington Railway. Fortunately, the ironwork was preserved and featured during the centenary celebration of the world's first railway in 1825. It was later displayed at the former rail museum at York, as shown in this photograph. In 1975, when the museum became the new National Railway Museum, it was moved and erected at its original site in West Auckland (UK). Robert Vogel, Smithsonian Institution, photographer
For years, the distinction of being the world's oldest surviving iron railway bridge has been accorded by scholars to the Gaunless Viaduct (1825), on display at the National Railway Museum, York (UK) (Figure 10). Designed by George Stephenson for the first railway, the 37 miles (23km) between Stockton and Darlington in north-east England, it consists of four 12.5ft (4m) lenticular truss spans with curved top and bottom chord members of 2.5in (6cm) diameter wrought-iron rods and five vertical iron posts cast integrally with the wrought-iron chord members. In the last 20 years an older bridge has been discovered in South Wales (UK) at Merthyr Tydfil, a major early 19th century iron-producing centre. Pont-y-Cafnau (Bridge of Troughs) is a unique cast-iron combined aqueduct tramroad bridge below the confluence of the Taff and Taff Fechan, built in January-June 1793 by Watkin George, Chief Engineer of the Cyfarthfa Ironworks, to carry an edge railway and water channel. An iron trough-like girder is carried in an A-frame truss of cast iron spanning 47ft (14.2m), held together by mortise-and-tenon and dovetail joints. The next extant iron railway bridge seems to be another recently discovered at Aberdare (1811), followed by Gaunless. The oldest still in service is Hall's Station Bridge, a Howe truss designed in 1846 by Richard Osborne, a London-born Irishman who worked as engineer for the Philadelphia & Reading Railroad, although its current use is vehicular and not rail. The first major iron truss with pin connections was built in the USA in 1859, and the earliest iron cantilever in Germany in 1867, over the Main at Hassfurt.
Figure 11 Bollman Bridge (c 1869), Savage, Maryland (USA). This pre-restoration photograph shows the paired stanchions located at mid-span that support the anchorage block where the radiating suspension stays all meet in pinned connection. The octagonal profile of the vertical and horizontal compression members was a design motif of Wendel Bollman, the bridge's designer. He, along with Albert Fink, who designed a similar type of structure known as the Fink truss, motivated the chief engineer of the Baltimore & Ohio Railroad, Benjamin Henry Latrobe III, to use iron bridges exclusively for the system's major spans. William Barrett, HAER Collection
Another important composite iron truss surviving from the early period of iron bridge construction is the Bollman bridge (c 1869) at Savage, Maryland (USA) (Figure 11).
Britannia Bridge (1850) across the Menai Straits, Wales (UK), designed by Robert Stephenson and William Fairbairn, was the prototype of the plate-girder bridge, eventually used throughout the world. Originally intended to be a stiffened suspension bridge of four spans, each span (459ft (140m) over the channel; 230ft (70m) land spans) consisted of paired rectangular wrought- iron tubes through which the trains passed. Although Navier published his theory of elasticity in 1826, so little was known of structural theory that Stephenson relied primarily on empirical methods of testing, modifying, and retesting a series of models to design the tubes. They were fabricated on site, floated into position, and raised into place by hydraulic jacks. Riveting was done both by hand and using pneumatic riveting machines invented by Fairbairn. So strong were the tubes that the suspension chains were abandoned. The bridge continued in service until irreparably damaged by fire in May 1970, when the world lost one of its most remarkable 19th century engineering monuments was lost, but the near-contemporary Conway Castle Bridge (1848) survives.
Although the 19th century was marked by significant technological progress, such breathtaking achievement had its price. Three- quarters of the way through the century, two events, one on either side of the Atlantic, sobered the engineering profession. These took the form of accidents: the Ashtabula, Ohio, bridge disaster of 1876 in the USA, and the Tay Bridge disaster in Scotland (UK) in 1879. Forewarnings had occurred in Europe as early as 1847, when one of Robert Stephenson's composite cast and wrought-iron girder bridges over the River Dee on the Chester & Holyhead Railway collapsed. Three years later, 478 French soldiers were pitched into the Maine at Angers when one of the anchoring cables of a suspension bridge embedded in concrete tore loose during a storm, mainly owing to resonance oscillation and by the oxidation of the iron wires. The Dee Bridge disaster spurred the development of malleable wrought-iron girders, thought to be of safer construction. Collapse of the Basse-Chaine Bridge resulted in a twenty-year moratorium on cable-suspension bridge construction in continental Europe.
Scientific analysis of bridge design during the 19th century
It took the worst bridge disasters of the century in the USA, Great Britain, and France to usher in the development of standards, specifications, and enough regulation to protect the travelling public. The loss of 83 lives caused by the collapse of a cast- and wrought-iron truss in Ashtabula prompted an investigation by the American Society of Civil Engineers. The loss of 80 lives by failure of a section of the two-mile-long Tay Bridge resulted in similar inquiries in Britain.
The reasons for these major failures were similar: ignorance of metallurgy resulted in uneven manufacturing methods and defective castings, and inadequate inspection and maintenance were inherent at both bridges. For the Tay Bridge, exceptionally strong vibrations due to dynamic wind stresses under a moving load created a lack of aerostatic stability and eventual failure. It took engineers another quarter-century to perfect bridge design according to advanced theories of stress analysis, understanding of material properties, and renewed respect for the forces of nature. A definitive understanding of the physical oscillations and vibrations of structures did not occur until the middle of the 20th century after the Tacoma Bridge collapse in the USA in1940.
Advances in design theory, graphic statics, and a knowledge of the strength of materials by engineers such as Karl Culmann and Squire Whipple were achieved in the second half of the 19th century, but the factor that most influenced the scientific design of bridges was the railroads. Engineers had to know the precise amount of stresses in bridge members to accommodate the thundering impact of locomotives. Founded on the pioneering work of the American Squire Whipple and other European engineers as Collignon, the last quarter of the 19th century witnessed broad application of both analytical and graphical analysis, testing of full-size members, comprehensive stress tables, standardized structural sections, metallurgical analysis, precision manufacturing and fabrication in bridge shops, publication of industry-wide standards, plans, and specifications, inspections, and systematic cooperation between engineers, contractors, manufacturers, and workers. The combined experience of the railroads, bridge manufacturing companies, and the engineering communities enabled the railroads successfully to tackle long-span iron and steel bridges and long-span trussed-roof train sheds, two engineering icons of the 19th century.
Figure 12 Whipple Truss Bridge (1867), Normanskill Farm, Albany, New York (USA), remains in service to this day, restricting only buses and trucks, thus testifying to the efficacy of Whipple's design. All members are original, their sizes determined by the forces they carried, deduced from scientific analysis.Smithsonian Institution
The first practical design solution was obtained independently in the USA by Squire Whipple in 1847, and in Russia by D I Jourawski in 1850. Whipple had been working on the problem since before 1841, when he patented and built his all-iron bowstring truss bridge, which proved exceptionally suitable for short highway and canal spans. His book on stress analysis, A Work on Bridge Building, is recognized as the USA's contribution to structural mechanics for the period. His major breakthrough was the realization that truss members could be analysed as a system of forces in equilibrium, assuming that a joint is a frictionless pin. Forces are broken down into horizontal and vertical components whose sums are in equilibrium. Known as the "method of joints," it permits the determination of stresses in all members of a truss if two forces are known. Whipple clearly outlined methods, both analytical and graphical, for solving determinate trusses considering uniformly distributed dead loads and moving live loads. Over a dozen of Whipple's bowstring trusses survive as elegant illustrations of his breakthrough conclusions (Figure 12).
The next advance was the "method of sections" published in 1862 by A Ritter, a German engineer. Ritter simplified the calculations of forces by developing very simple formulae for determining the forces in the members intersected by a cross-section. The third advance was a better method of graphical analysis, developed independently by James Clerk Maxwell, Professor of Natural Philosophy at King's College, Cambridge (UK), published in 1864, and Karl Culmann, Professor at the newly established Federal Institute of Technology (Eidgenossische Technische Hochschule) in Zürich (Switzerland), who published his methods in 1866. The solution of bending in a cantilever was developed over a long period of time, starting with Galileo's famous illustration of the wooden beam, anchored in the ruinous masonry wall, holding a stone weight at its end. Although it was not entirely accurate, subsequent solutions were discussed in terms of Galileo's cantilever. C A Coulomb in France hypothesized in 1776 that the flexural stress in a cantilevered beam had a maximum value in compression on the bottom edge and a maximum value in tension on the top with a neutral axis somewhere between the two surfaces. The problem of understanding bending moments in mechanical terms was described by Louis Marie Henri Navier in his Résumé de leçons données à l'École des Ponts et Chaussées in 1826. The Swiss mathematician Leonard Euler provided the solution to the elastic buckling of columns as early as 1759.
Railroad viaducts and trestles
Railroads, the transportation mode that revolutionized the 19th century, generated a bridge type that merits special attention. The limited traction of locomotives forced the railroad engineer to design the line with easy gradients. Viaducts and trestles were the engineering solution for maintaining a nearly straight and horizontal line where the depth and width of the valley or gorge rendered embankments impracticable. These massive, elevated structures were first built in Roman style of multiple-stone arches and piers. Later, when wrought iron and steel became available, engineers built viaducts and trestles of great length and height on a series of truss spans or girders borne by individual framed towers composed of two or more bents braced together.
Figure 13 Thomas Viaduct (1835), Relay, Maryland (USA). This illustration from The United States Illustrated, published in the 1850s, shows the heroic proportions of this massive stone structure, constructed while the Baltimore & Ohio Railroad was still influenced by the British precedent of strong, durableconstruction.Smithsonian Institution
The Thomas Viaduct on the Baltimore & Ohio Railroad (1835) (Figure 13), the Canton on the Boston & Providence Railroad (1835), and the Starrucca on the New York & Erie Railroad (1848) are the oldest stone viaducts and three of the great monumental structures of the USA's early railways. Examples in Europe include the Viaduc de Barentine (1846), constructed by British navvies under the direction of MacKenzie and Thomas Brassey in brick rather than stone, and the Viaduc de Saint-Chamas (1847), both in France. In the United Kingdom, notable viaducts include the 181ft (55m) Ballochmyle Viaduct (1848), designed by John Miller for the Glasgow & South Western Railway, the largest masonry-arch span in the country; the Harrington Viaduct (1876), the longest at 3500ft (1067m), carried on 82 brick arches; the Meldon Viaduct (1874), the best surviving iron viaduct in Devon; and, in concrete, the Glenfinnian Viaduct (1898), which has 21 arches of mass-poured concrete.
Most notable of the early trestles was the Portage Viaduct in the USA (1852), a remarkable timber structure designed by Silas Seymour, carrying the Erie Railroad over the Genessee River, 234ft (71m) above the water and 876ft (276m) long (Figure 14). It was destroyed by fire in 1875, to be replaced in iron, and later in steel. One of the first iron viaducts was the 1673ft (510m) long Crumlin Viaduct (1857), constructed by Thomas W Kennard and designed by Charles Liddell for the Newport-Hereford line, 217ft (66m) above the Ebbw Vale in Wales (UK). It served as the prototype for later ones, such as the Viaduc de la Bouble (1871), a series of lattice girders on cast-iron towers flared at the bottom, built under the direction of Wilhelm Nordling. It was 1296ft (395m) long by 216ft (66m) high on the Commentry-Gannett line in France.
Figure 14 Portage Viaduct (1852) (USA), photographed shortly after it was completed for this stereoscopic view, was the wonder of visiting engineers, who used it frequently as an example of American timber bridge construction technology in European texts Eric DeLony, photographer
Figure 15 Kinzua Viaduct (1900), located on the Bradford Branch in a remote region near the town of Kushequa in north-west Pennsylvania (USA), was originally constriucted in 1882 by the New York & Erie Railroad to service lumber mills in this lush, forested corner of Pennsylvania. The present structure, 302ft (92m) high and 2052ft (625m) long, replaced the original when Erie officials decided that the bridge could no longer support their heavier trains. Today the viaduct forms the main attraction of a state park. Jack Boucher, HAER Collection
The first viaduct of iron in the USA was designed by Albert Fink for the Baltimore & Ohio Railroad over Tray Run in the Cheat River valley in (West) Virginia, a remote, wild, yet picturesque site in the wilderness. Dating from 1853, it was a series of inclined cast-iron columns resting on stone pedestals connected at the top by cast-iron arches, the whole system braced by wrought-iron ties. Examples surviving today in North America include the Kinzua Viaduct (1900) on the former Erie Railroad in Pennsylvania (Figure 15), and the Lethbridge Viaduct (1909) on the Canadian Pacific in Alberta, composed of alternating 67ft (20m) trestles and 100ft (30m) girders, at 5327ft (1624m) long the longest and heaviest in the world. The Tunkhannock Viaduct (1915), 240ft high (73m) by 2375ft long (724m), is the largest reinforced concrete-arch bridge in the world.
Although suspension bridges had been known in China as early as 206 BC, the first chain suspension bridge did not appear in Europe until 1741, when the 70ft (21m) span Winch Bridge was constructed over a chasm of the River Tees (UK), with the flooring laid directly on two chains. It was an American, James Finley, however, who built the first practical suspension bridge in 1796 in the USA. This was a bridge over Jacobs Creek near Uniontown, Pennsylvania, which Finley described as a "stiffened" bridge in an article he published in Portfolio in 1810. The span displayed all the essential elements of the modern suspension bridge: a level deck hung from a catenary system suspended over towers and anchored in the ground, and a truss-stiffened deck, resulting in a rigid bridge capable of supporting relatively heavy loads.
The world's first wire-cable suspension bridge was a 408ft (124m) temporary footbridge built in 1816 for the workers of wire manufacturers Josiah White and Erskine Hazard over the Schuylkill in Philadelphia. The USA contributed little more until the middle of the century, but these inventions were immediately followed up in Europe. The French and Swiss continued to use wire cables, developing methods of fabricating the cables in situ. In 1822, Marc Séguin proposed a suspension cable made up of one hundred thin iron wires, erected his first suspension bridge (actually a catwalk like the White and Hazard bridge) over the Cance at Annonay, and proposed a major structure over the Rhône at Tournon. By scientific testing, he proved the strength of the wire cable - twice that of the English iron eyebar chain - and described all in Des ponts en fil de fer, published in 1824. The world's first permanent wire-cable suspension bridge, designed by Séguin and Guillaume-Henri Dufour, was opened to the public in Geneva in 1823, followed by Séguin's Tain-Tournon Bridge, a double suspension span over the Rhône, completed in 1825. Its 1847 replacement still stands, probably the oldest wire-cable suspension bridge in the world, with its carefully replicated wooden stiffening truss and deck. Several of Séguin's first-generation wire-cable suspension bridges, dating from the 1830s, remain over the Rhône at Andance and Fourques, but the decks have been replaced with steel. Wire cable attained its place as the system par excellence for long-span bridges in 1834, with the 870ft (265m) Fribourg Bridge, designed by Joseph Chaley over the Sarine in Switzerland. From this developed the typical European standard - cables of parallel, thin wires, light decks stiffened by wooden trusses, piers and abutments sunk - using hydraulic cement - of which hundreds were built.
Figure 16 Menai Suspension Bridge (1826)(UK) sat on massive stone piers and viaduct approaches to gain the 50ft (15m) clearance required by the British Admiralty for the passage of ships. Shunsuke Baba, photographer
The British preferred to use chains of linked eyebars, and achieved spans of lightness and grace, all the more effective in contrast with the colossal masonry suspension towers. The United Kingdom's first large-scale suspension bridge was the Menai Bridge on the London to Holyhead road over the straits of the same name in North Wales (Figure 16). Travellers would board a ship at Holyhead for the final leg of the trip to Ireland. It was designed by Thomas Telford and completed in 1826, with an unprecedented span of 580ft (177m) using wrought-iron eyebars, each bar being carefully tested before being pinned together and lifted into place. The roadway was only 24ft (7m) wide and, without stiffening trusses, soon proved highly unstable in the wind. The Menai bridge was twice rebuilt before the entire suspension system was replicated in steel in 1940 and the arched openings in the towers were widened. The oldest suspension bridge extant today is the Union Bridge over the River Tweed at Berwick (UK), a chain-link bridge designed and erected by Captain Samuel Brown in 1820, with a span of 449ft (137m).
With the French declaring a moratorium on suspension-bridge construction following the collapse of the Basse-Chaine Bridge in 1850, the creative edge passed back across the Atlantic, to be picked up by Charles Ellet and John Augustus Roebling in the USA. After studying suspension bridges in France, Ellet returned with the technology and built a 1010ft (308m) bridge over the Ohio River at Wheeling, (West) Virginia, in 1849, which was the longest in the world. Thanks to techniques developed by the Roeblings and used in the structure's rebuilding, following a storm that ripped the cables off their saddles, the bridge remains in service today.
Figure 17 Niagara Bridge (USA), whose completion in 1855 vindicated John Roebling's conviction that the suspension bridge would work for railroads, lasted nearly half-a-century before it had to be replaced in 1896. At mid-century, it was the only form capable of uniting the 821ft (250m) gorge in a single span. This half-stereoscopic viewshows the massive stiffening trusses and the wire-cable stays that tied the deck superstructure to the walls of the gorge. Eric DeLony Collection
Roebling had arrived in the USA ten years earlier and established a wire-rope factory in Saxonburg, Pennsylvania, which he later moved to Trenton, New Jersey. Educated in Europe, he would have been exposed to the concepts of wire-cable suspension bridge engineering of the French and Swiss. He and Ellet competed for primacy in suspension bridge design. Roebling won out when he took over design of the Niagara Suspension Bridge from Ellet, successfully completing it in 1855 (Figure 17).
The inherent tendency of suspension bridges to sway and undulate in wavelike motions under repeated rhythmic loads such as marching soldiers or the wind was not completely understood by engineers until the 1940s, following the collapse of the Tacoma Narrows Bridge ("Galloping Gertie"). Credit for designing the first suspension bridge rigid enough to withstand wind loads and the highly concentrated loadings of locomotives belongs to John Roebling. His first masterpiece was the Niagara Suspension Bridge, with a span of 821ft (250m) on the Grand Trunk Railway below Niagara Falls. The two decks, the upper for the railway and the lower for common road service, were separated by an 18ft (6m) stiffening truss. In addition, the truss was braced with radiating cable stays inclined from the tops of the suspension towers and anchoring cables tying the deck to the sides of the gorge, arresting any tendency to lift under gusts of wind. For the four main cables, Roebling used parallel wires laid up in place but, instead of individual strands like the "garland" system preferred by the French, he bunched the strands together in a single large cable and wrapped them with wire, a technique he patented in 1841 but one that Vicat had illustrated in 1831 in his Rapport sur les ponts en fil de fer sur le Rhône.
Few bridges in the world built since the Brooklyn Bridge in New York (USA) can stand entirely clear of its shadow. Completed in 1883, the plan involved two distinctive stone towers, four main cables, anchorages, diagonal stay cables, and four stiffening trusses separating the common roadway and trolley line from a pedestrian promenade. With a record-breaking span of 1595ft (486m), the Brooklyn Bridge was designed by John Roebling, but it was built by his son and daughter-in-law after he died of blood poisoning following an accident while surveying the location of the Manhattan tower in which his foot was crushed. Massive Egyptian towers, pierced by pointed Gothic arches, stand 276.5ft (84m) above mean high water and 78.5ft (24m) below on the Manhattan side, 44.5ft (14m) on the Brooklyn. Diagonal stay cables give the bridge its distinctive appearance, but function to stiffen the deck. It took two years to lay up each of the four 15.75in (40cm) diameter main cables with 5434 wires, the pioneer use of steel wire (Figure 18).
Figure 18 Brooklyn Bridge (1883) still serves as a majestic portal to Manhattan (USA) for travelers coming from Brooklyn and for ships as they approach from the harbour. The bridge is indelibly linked with New York and, along with San Francisco's Golden Gate, symbolically represents these two famous American cities. Jack Boucher, HAER Collection
Figure 19 Delaware Aqueduct (1849) was being used as a toll bridge in 1969 when it was recorded by the Historic American Engineering Record (HAER), the USA's official engineering heritage program. The towpath of the wooden canal trunk would have been level with the upper most set-back of the masonry piers. David Plowden, HAER Collection
Two other Roebling suspension bridges survive, both recently rehabilitated. One spanning the Ohio River at Cincinnati was completed in 1867. The 1849 Delaware Aqueduct was designed to carry a wooden trunk of water on the Delaware & Hudson Canal. The latter was carefully rehabilitated by the US National Park Service and is the oldest surviving suspension bridge in the USA (Figure 19).
Structural steel is stronger and more supple than cast or wrought iron, and allowed greater design flexibility. The last thirty years of the 19th century witnessed the phasing in of steel plates and rolled shapes, leading to the enormous production of steel trusses and plate-girder spans of ever-increasing lengths throughout the world. Steel arches and cantilevers were favoured for long spans because they better withstood the impact, vibration, and concentrated loads of heavy rail traffic.
The earliest known use of steel in bridge construction was the 334ft (102m) suspension span across the Danube Canal (1828) near Vienna (Austria), designed by Ignaz von Mitis. The steel eye-bar chains were forged from decarburized iron from Styria. Steel halved the weight of wrought iron, but remained prohibitively expensive for another forty years before steelmaking processes such as the Bessemer and the open-hearth were perfected (it is uncertain whether the Styrian ironmasters created real steel or whether the decarburization was a mechanical process resulting in a surface-hardened steel, a kind of wrought iron rather than the mass steel that results from the Bessemer process). The first major bridge utilizing true steel was the Eads Bridge (1874), the most graceful of the Mississippi River crossings in the USA, built by the Keystone Bridge Company, which subcontracted fabrication of the steel parts to the Butcher Steel Works and the iron parts to Carnegie-Kloman, both of Pittsburgh. Its ribbed, tubular steel arch spans of 502ft, 520ft, and 502 ft (153m, 159m, and 153m) and double-decked design shattered all engineering precedents for the time: the centre span was by far the longest arch. Mathematical formulae for the design were developed by Charles Pfeiffer. The cantilever method of erection, devised by Colonel Henry Flad and used for the first time in the USA, eliminated the centring that would have been impossible in the wide, deep, and fast-flowing Mississippi. While recovering from illness in France, the designer James Buchanan Eads found the solution to sinking piers in deep water. He investigated a bridge under construction over the Allier at Vichy that used Cubitt and Wright's pneumatic caissons - floorless chambers filled with compressed air.
The first major bridge of steel in France was the Viaur Viaduct (1902), a three-hinged steel arch of 721ft (220m) flanked by 311ft (95m) cantilevers. The crowning achievement of the material during the 19th century, however, was the mighty Forth Railway Bridge in Scotland (1890). Its design was motivated by the Tay Bridge disaster. About 54,000 tons of Siemens-Martin open-hearth steel were required for the 1710ft (521m) cantilever spans whose main compression struts of rolled steel plate were riveted into 12ft (4m) diameter tubes. Another authority on the effects of wind on structures was Gustav Eiffel, who conducted similar experiments in France prior to designing another of the world's great arch bridges, the 541ft (165m) Garabit Viaduct (1885) in the windy valleys of the Massif Central, though he held to wrought iron, not being convinced of the efficacy of the new material.
Steel arches of enormous span were built during the first few decades of the 20th century. One of the greatest is the Hell Gate Bridge in the USA (1917), a two-hinged trussed arch, the top chord of which serves as part of a stiffening truss. Designed by Gustav Lindenthal to span the Hell Gate at the northern tip of Manhattan Island for the New England Connecting Railroad, it is framed between two massive stone towers. The 978ft (298m) arch, weighing 80,000 tons (81,280 tonnes), was the longest and heaviest steel arch in the world. The next was Bayonne Bridge (1931), which remains one of the longest steel arches in the world today. It was built during the Depression by a team assembled under the direction of Swiss-born and educated engineer, Othmar Ammann, chief engineer of the Port Authority of New York, one of the remarkable public works organizations of the USA, if not the world. Opening three weeks after the George Washington Bridge, then the longest suspension bridge in the world, this second record-breaking span was financed and built by the Port Authority simultaneously, the two projects forming one of the greatest public work endeavours since Roman times. The Bayonne Bridge connects Bayonne (New Jersey) and Staten Island (New York) with a manganese-steel parabolic two-hinged arch of 1675ft (511m) span and 266ft (81m) rise, the deck clearing high water by 150ft (46m). As in the Hell Gate, the arch's top chord acts as a stiffener, the bottom chord carrying the load. The Bayonne Bridge was designed to be 25ft (8m) longer than the nearly identical Sydney Harbour Bridge in Australia, started five years earlier.
Bridges in areas other than Europe and the USA should be investigated, as the colonial empires of several nations were at their peak during the autumn years of the 19th century. In India, for example, the British built several long-span railway bridges, such as the Hooghly and the Sukkur bridges which exceeded 1000ft (300m) in span and are interesting because they were constructed using the simplest equipment and armies of unskilled labour.
This structural form was mentioned in the previous section on steel bridges in the discussion of the Eads Bridge, where the erection of the arches employed principles of the cantilever, and the Forth Railway Bridge, perhaps the world's greatest cantilever. A discussion of this type of bridge is warranted because of its engineering interest and because the form illustrates the outstanding application of iron and steel to bridge construction.
Cantilevers were one of the first bridge types, many being built by the ancient cultures of China and India. The first modern cantilever was Heinrich Gerber's Hassfurt Bridge over the Main in Germany (1867), with a central span of 124ft (38m). It was a continuous girder hinged at the points of equal resistance where the moments of the uniform load were zero. According to W Westhofen, who wrote the classic account of the Forth Bridge, the idea first was suggested by John Fowler, co-designer of the Forth Bridge, around 1846-50. In Britain and the USA the form was known as cantilevers, in France as portes-à-faux, and in Germany as the Gerber Bridge, named after the builder. By inserting hinges, the continuous girder can be made statically determinant. This was their first attribute, but later as the possibility of erection without scaffolding was recognized - the ability of the arms of the bridge to be built out from the piers, balancing each other without the need for falsework. This became the great advantage. The principle also is applicable to other bridge types such as arches, an example being the Eads Bridge, where the width, depth, and current of the mighty Mississippi prevented the erection of falsework.
In 1877, C Shaler Smith provided the first practical test of the principle when he built what then was the world's longest cantilever over a 1200ft (366m) wide and 275ft (84m) deep gorge of the Kentucky River near Dixville, Kentucky (USA). The cantilever resolved the difficulty of erecting falsework in a deep wide gorge. The anchor arms were 37.5ft (11m) deep Whipple trusses that extended 75ft (23m) beyond the piers. From these were hung 300ft (91m) semi-floating trusses fixed at the abutments and hinged to the cantilever, making the overall span from pier to abutment 375ft (114m). The bridge was rebuilt in 1911 by Gustav Lindenthal using the identical span lengths, but with trusses twice as deep.
The next important cantilever was a counterbalanced span designed by C C Schneider for the Michigan Central Railroad over the Niagara Gorge in 1883. With arms supporting a simple suspended truss, this 495ft (151m) span and the nearly identical Fraser River span in British Columbia (Canada) directed the attention of the engineering world to this new type of bridge. These two were the prototypes for subsequent cantilevers at Poughkeepsie, New York, the Firth of Forth Bridge in Scotland, and the Québec Bridge in Canada.
The Poughkeepsie Cantilever (1886) was the first rail crossing of the Hudson River below Albany, 55 miles (89km) north of New York City. Built by the Union Bridge Company of New York to designs by company engineers Francis O'Rourke and Pomeroy P Dickinson, the overall length is 6768ft (2063m), including two cantilevers of 548ft (167m) each. Strengthened in 1906 by adding a third line of trusses down the middle designed by Ralph Modjeski, citizens on both sides of the river are working to have this magnificent, but now abandoned, bridge incorporated as part of the Hudson Greenway trail system.
Figure 20 Forth Bridge (1890): an historic photograph showing the FifeTower at North Queensferry, Scotland (UK), nearing completion. The illustration is from Wilhelm Wethofen's article published in Engineering Magazine, 28 February 1890.
The world's most famous cantilever also is one of the world's first and largest steel bridges and held the record for longest cantilever for 27 years. Pontists are familiar with the brilliant demonstration used by Sir Benjamin Baker to illustrate the structural principles of the Firth of Forth Bridge: two men sitting on chairs with outstretched arms and sticks supporting Kaichi Watanabe, a visiting engineering student from Japan, sitting on a board, representing the fixed piers, cantilevers, and suspended span. To ensure that there was no repeat of the Tay disaster, Baker conducted a series of tests, gauging wind at several sites in the area over a two-year period, arriving at a design pressure of 56lb/ft2 (274kg/m2), which was considerably in excess of any load the bridge would ever sustain. Each of the two main spans of the bridge consists of two 680ft (207m) cantilevers with a 350ft (107m) suspended span for a total length of 1,710ft (521m). John Fowler and Benjamin Baker designed the Forth Bridge (1890) to resist wind loads 5.5 times those that toppled the Tay Bridge (Figure 20).
The Forth Bridge's record was broken in 1917 when the Québec Bridge was finally completed, spanning the St Lawrence River near Québec (Canada) with an 1800ft (549m) cantilever span. Its predecessor failed in 1907 while under construction, killing 82 workmen and ending the career of one of America's most prominent engineers. Theodore Cooper had taken the commission reluctantly with a fee insufficient to hire assistants, to allow for written specifications, or to provide for on-site inspections. The design was not recalculated when Cooper, intent on exceeding the span of the record-holding Forth Bridge, increased it from 1600ft to 1800ft, which was ultimately to result in the failure of one of the main compression members of the lower chord in the south anchor. The second bridge also had its problems as well when one of the jacks failed while lifting the 5000 ton centre suspended span, dropping it into the river. A duplicate truss was successfully lifted into place within two weeks and the bridge was finally opened. This bridge, designed by E H Duggan and Phelps Johnson with Ralph Modjeski as consultant, was criticized by many engineers as being the ugliest, while the cantilever was generally regarded as a type, especially those of American origin, whose profile was unsightly despite their record lengths.
The largest cantilever in Europe was Saligney's Danube Bridge near Czernavoda (Romania), with a span of 623ft (190m). Another great cantilever is the Howrah Bridge over the Hooghly River at Calcutta (India), with a span of 1500ft (457m).
Reintroduction of masonry and concrete
Concrete is an ancient material. It was first discovered and used by the Romans in their aqueducts and temples, to be sporadically rediscovered throughout time by engineers who used it in its mass- poured form. The discovery of natural cement in 1796, on the Isle of Sheppey in the Thames Estuary (UK), renewed interest in the material, but the age of concrete began its most vigorous development with Joseph Aspdin's invention in 1824 of artificial Portland cement. This mixture of clay and limestone, calcined and ground, resulted in a material having broad application for buildings and bridges. The scientific studies of Vicat on natural and artificial cements initiated in 1816 at the Pont de Souillac (France) revealed the first understanding of the chemical properties of hydraulic cement. Canvass White, an engineer on the Erie Canal (USA), discovered natural cement in 1818 and established a mill to manufacture the substance at Chittenango, New York. The primary benefit of the material was its ability to set under water. Naming it hydraulic cement, he patented the process in 1819 and used it for aqueducts, abutments, culverts, and lock walls.
In 1831, Lebrun, a French engineer, designed the first concrete bridge to span the River Agout, although it never was built. A significant early structural use of concrete in the USA was in 1848 for the foundations and deck of the Starrucca Viaduct on the New York & Erie Railroad, a mighty stone-arched bridge with an overall length of 1040ft (317m), designed by Julius Walker Adams and built by James Pugh Kirkwood.
Later, the use of artificial cement combined with more sophisticated understanding of the mathematical principles of arch theory resulted in renewed interest in stone and masonry arch bridges in Europe. Beginning in the mid-19th century, masonry railroad viaducts were an important civil engineering technology for continental Europe. The most impressive were the 1969ft (600m) long Chaumont Viaduct (1857) and the 240ft (73m) high Sainte-Brieuc (Barentin) Viaduct (1860), both in France, and the Goltzschtal Viaduct in Germany, which used 26 million units of brick.
The French engineer, Paul Séjourne, expressed the most elegant modern restatement of the principles of this most ancient material in his masterpiece bridges of stone, the 279ft (85m) span Pont Adolphe in Luxembourg (1903) and the bridge at Plauen, Germany (1905), which was the longest ever achieved in stone masonry, with a span of 295ft (90m).
The beginning of concrete as a major material of bridge construction dates from 1865, when it was used in its mass, unreinforced form for a multiple-arch structure on the Grand Maître Aqueduct conveying water from the River Vanne 94 miles (151km) to Paris. Engineers in the late 19th century demonstrated the possibilities of reinforced concrete as a structural material. With concrete resisting compressive forces and wrought iron and steel bars carrying tension, bridges of dramatic sweeping curves evolved. Today's long-span reinforced- concrete bridges are descended from French gardener Joseph Monier's flower pots and his numerous bridge patents granted between 1868 and 1878. He is credited with being the first to understand the principles of reinforced concrete when in 1867 he patented plant tubs of cement mortar strengthened with iron-wire mesh embedded in the concrete and moulded into curvilinear forms. Not being an engineer, he was not permitted to build bridges in France and so he sold his patents to German and Austrian contractors Wayss, Freitag and Schuster, who built the first generation of reinforced concrete bridges in Europe: the Monierbrau 131ft (40m) footbridge in Bremen (Germany) and the Wildegg Bridge, with a span of 121ft (37m), in Switzerland. Additional patents were granted in Belgium, France and Italy, especially to the Frenchman François Hennebique, who established the first international firm to market his bridges before World War I. His first masterpiece was built at Millesimo (Italy) in 1898, and that at Châtellérault in France (1900) remains as one of the first notable reinforced concrete arch bridges in the world, with a central span of 172ft (52m) and two lateral arches of 131ft (40m). In 1912, Hennebique set a new world record with a bridge over the Tiber in Rome (Italy) with a span of 328ft (100m). Other important three-span bridges with impressive central spans were built in France by Eugène Freyssinet, such as the bridges at Veurdre (1910) and Boutiron (1912).
In France, where much of the original thinking on reinforced concrete occurred, the record span was the Saint-Pierre du Vauvray Bridge (1922) by Freyssinet. He perfected the technique of prestressing concrete by inserting hydraulic rams in a gap left at the crown of arches, then activating the rams to lift the arches off the falsework and filling the gap with concrete, leaving only permanent compressive stresses in the arches. The Vauvray Bridge over the Seine was the record span at 430ft (131m), the deck being hung from hollow cellular arch ribs on wire hangers, coated with cement mortar, and supporting the road on light concrete deck trusses. The Vauvray Bridge was destroyed in World War II, leaving the Plougastel Bridge (1930) over the River Elon at Brest, with three spans of 567ft (173m), as the longest reinforced concrete arch span until 1942.
Swiss engineer Robert Maillart designed three-hinged arches in which the deck and the arch ribs were combined to produce closely integrated structures that evolved into stiffened arches of very thin reinforced concrete and concrete slabs, as at the Schwandbach Bridge (1933), near Schwarzenbach (Switzerland). Maillart's early apprenticeship with Hennebique sharpened his awareness of the plastic character of the material. His profound understanding of reinforced concrete allowed him to develop new, light, and magnificently sculptural forms. Maillart's bridges are of two distinct types: stiffened-slab arches and three-hinged arches with an integrated road slab. The 295ft (90m) Salginatobel Bridge (1930) near Schiers (Switzerland) is the most spectacular and classic example of this type in the world.
The world's longest concrete and masonry arch bridge is the Rockville Bridge (1902), which carries four tracks of the former Pennsylvania Railroad over the Susquehanna River (USA) on 48 arches, 70ft (21m) each, for a total length of 3820ft (1164m). It was part of a massive twenty-year improvement programme under the direction of William H Brown, chief engineer. The largest all- reinforced concrete bridge, however, is the Tunkhannock Viaduct (1915) built by the Delaware, Lackawanna & Western Railroad in north-eastern Pennsylvania (USA), composed of ten semi-circular double-arch spans of 180ft (55m) with the spandrels filled with eleven smaller arches. Like Rockville, it was a major component in another early 20th century US railroad improvement project, this time a massive realignment. Abraham Burton Cohen was the rail line's designer of the reinforced-concrete bridges.
The first major reinforced-concrete bridge in the United Kingdom was the Royal Tweed Bridge (1928), made up of four rhythmic open- spandrel arches filled with vertical posts increasing in span from 167ft (51m) to 361ft (110m) as the roadway climbs from low to high embankments on each side of the river.
Sweden is another country that excelled in building elegant and innovative reinforced-concrete arch bridges of extremely long span. The first was the Traneberg Bridge (1934) in Stockholm, designed by Harbour Board engineers Ernst Nilsson and S Kasarnowsky with Eugène Freyssinet consulting. Its 593ft (181m) span was surpassed briefly in 1942 by the Esla Bridge in Spain with a span of 631ft (192m), but within the same year the title for the longest arch was regained for Sweden by S Haggböm with the Sando Bridge, the longest reinforced- concrete arch in the world at 866ft (264m).
Moveable and transporter bridges
This essay ends with two of the oldest types of bridges known to humankind. The bascule or draw span was developed by Europeans during the Middle Ages. There was a resurgence of moveable bridges during the late 19th century. Reliable electric motors and techniques for counterbalancing the massive weights of the bascule, lift, or swing spans marked the beginning of modern moveable-bridge construction. They are usually found in flat terrain, where the cost of approaches to gain high-level crossings is prohibitive, and their characteristics include rapidity of operation, the ability to vary the openings depending on the size of vessels, and the facility to build in congested areas adjacent to other bridges.
Completion of Tower Bridge over the Thames in London (1894), a 260ft (79m) roller-bearing trunnion bascule and the best known bascule bridge in the world, and Van Buren Street Bridge in Chicago, the first rolling lift bridge in the USA (patented by William Scherzer), marks the efficient solution to problems of lifting and locking mechanisms. In 1914, the Canadian Pacific Railroad completed the world's largest double-leaf bascule, spanning 336ft (102m) over the ship canal at Sault-Sainte-Marie, Michigan, rebuilt with identical spans in 1941. The Saint Charles Airline Railway Bridge (1919) spanning 16th Street in Chicago was at 260ft (79m) the longest single-leaf bascule when it was completed. In 1927, the Atchison, Topeka & Santa Fe Railroad built the world's longest single-span swing bridge, 525ft (160m), over the Mississippi at Fort Madison, Iowa. One of the most interesting and unusual moveable bridges is the Lacey V Murrow Bridge (1940), whose design reached back to the pontoons built by Roman legions. The depth and breadth of the lake precluded the construction of conventional piers on pilings, cantilever, or suspension spans, and so Washington State bridge engineers designed a floating bridge supported by hollow concrete pontoons to connect Seattle and Mercer Island. Equally unique was the retractable floating draw span for ocean-going ships in the lake. Three other bridges of this type were completed over the Hood Canal (1961) and at Evergreen Point (1963). A span parallel to the Murrow Bridge now carries the increased traffic of Interstate Highway 90.
A comparable example of an unusual type of moveable bridge in Europe is the transporter bridge, where a platform suspended by cables from tall towers and superstructure is carried on an overhead framework. This type of bridge also reaches back into history, integrating ancient technology such as the rope ferry with new structural forms and materials such as the iron beam and the strongest steel cables. The transporter bridge was the original solution to spanning the mouth of a river or entrance to a harbour and also served as a monumental gateway. Although it was patented in the UK and the USA in the mid 19th century, the first significant example was built by French engineer Ferdinand Arnodin, at Portugalete (1893) in Spain. Arnodin also invented the twisted steel cable, an important innovation for this type of bridge. The only other survivors are located in the United Kingdom at Middlesbrough and Newport (Wales) and at Martrou (France).
The author deeply appreciates the review and comments on this essay by the following individuals: Dr Shunsuke Baba (Faculty of Environmental Science and Technology, Okayama University, Japan), Professor Louis Bergeron (École des Hautes Études en Sciences Sociales, Paris, France), Sir Neil Cossons (Director, Science Museum, London, UK), Dott. Roberto Gori (Università di Padova, Italy), Dr Emory Kemp (Director, Institute for the History of Technology and Industrial Archaeology, West Virginia University, USA), Dr Michael Mende (Hochschule für Bildende Kunst, Braunschweig, Germany), David Simmons (Editor, Timeline, Ohio Historical Society, Columbus, USA), Dr Itoh Takasaki (Research Institute of Science and Technology, Nihon University, Japan), and Robert Vogel (Curator Emeritus, Museum of American History, Smithsonian Institution, Washington, DC, USA).
He is especially indebted to Michel Cotte (Tournon, France), whose review provided insights on bridge types, chronological structure, and other subtleties of European bridge history that the author was not aware of. His thorough review gives this paper a solid European foundation.
POTENTIAL WORLD HERITAGE BRIDGES
Clapper Bridges (Bronze Age): Dartmoor, Devon, England (UK)
Bridges of twisted vines & creepers: India, Africa, South America
Ponte Saint-Martin (c 25 BC): near Torino (Italy)
(*)Puente Romano (1 BC, AD 5): Mérida (Spain)1
Alcantara Bridge (AD 98): near Cáceres (Spain)2
Ancient cantilevers: Japan, China, Tibet3
Zhaozhou Bridge (c 605): Beijing vicinity (China)
Phra Bhutthos (12th century): Kompong Kdei vicinity (Cambodia)4
Jiangdonggiao (1565): (China)5
Shogun's Bridge (1638): Nikko (Japan)
Bridge of Khaju (1667): Isfahan (Iran)
Kintaikyo (1673): Iwakuni (Japan)
(*)Bridge over the Tigris (1065): Diyarbakir (Turkey)
(*)Bridge over the Batman River (1146), Malabadi (Turkey)
(*)Steinerne Brücke (1146): Regensburg (Germany)
Monnow Bridge (1272, 1296): Monmouth, Wales (UK)
(*)Puente del Diablo (1290): Martorell, Barcelona (Spain)
(*)Arabic Bridge (14th century): Arevalo, Ávila (Spain)
(*)Ponte della Maddalena (1345): Borgo a Mazzano, Tuscany (Italy)
Ponte Vecchio (1345): Florence, Italy6
Pont d'Avignon (c 1350): France
Pont Valentré (1355): Cahors (France)
(*)Karluv Most (1357): Prague (Czech Republic)
Renaissance and Neo-Classical
(*)Old Bridge over the Main (1543): Würzburg (Germany)
Ponte Santa Trinità (1569): Florence (Italy)
Rialto Bridge (1591): Venice (Italy)
Pont Neuf (1607): Paris (France)7
Aqueduct at Tomar (1613) and Elvas (1622): Portugal
Ratisbonne Bridge over the Danube: Germany (nd)
Dresden Bridge: Germany (nd)
Bridge over the Gironde: Bordeaux (France) (nd)
Pontypridd Bridge (1756): South Wales (UK)
(*)Kapellenbrücke (1333), Paintings (1611): Lucerne (Switzerland)
Bassano Bridge (1561, 1948): Bassano della Grappa (Italy)
Rumlangbrücke (1766): Switzerland
(*)Bridge over the Rhine (piers 1580, wood superstructure c 1800): Sackingen (Switzerland/Germany)
(*)Bridge over the Rhine (1804): Reinhau (Switzerland)
(*)Bridge over the Rhine (1816): Diessenhofen (Switzerland/Germany)
(*)Bridge over the Jagst (early 19th century): Unterregenbach (Germany)
Bridgeport Bridge (1862): Grass Valley, California (USA)
Cornish-Windsor Bridge (1866): New Hampshire/Vermont (USA)
Cast-iron arches in Tsarskoye Selo (18th century): St Petersburg (Russia)8
Decorative bridges (18th century): Ducal Gardens of Wörlitz, Dessau (Germany)9
Pont-y-Cafnau aqueduct and tramway bridge (1793): Merthyr Tydfil, Wales (UK)10
Pontcysyllte Aqueduct (1795): Llangollen, Wales (UK)
Rio Cobre Bridge (1800): Spanish Town (Jamaica)
Gaunless Viaduct (1825): National Railway Museum, York, England (UK)
Dunlaps Creek Bridge (1839): Brownsville, Pennsylvania (USA)
Laves Beam Bridge (1844): Royal Gardens, Hannover (Germany)
Philadelphia & Reading Railroad, Hall's Station Bridge (c 1846): Pennsylvania (USA)
Conwy Castle Bridge (1848): Wales (UK)
High Level Bridge (1849): Newcastle upon Tyne, England (UK)
Royal Albert Bridge (1859): Saltash, Cornwall, England (UK)
(*)Waldshut-Koblenz Railroad Bridge over the Rhine (1859): Switzerland/Germany
Cast-iron arches in Central Park (1860s): New York City (USA)
(*)Kleve-Griethausen Bridge over the Lower Rhine (1865): Germany
Whipple Truss Bridge (1867): Normanskill Farm, Albany, New York (USA)
Baltimore & Ohio Railroad, Bollman Truss Bridge (c 1869): Savage, Maryland (USA)
(*)Schwedler Arch-Truss Railroad Bridge over the Elbe (1873): Langendorf (Germany)
Ponte Ferroviaria de Dona Maria Pia (1877): Italy
(*)Maria Pia Bridge (1877): Oporto (Portugal)
(*)Dom Luiz I Bridge (1886): Oporto (Portugal)
Railroad Viaducts & Trestles
Baltimore & Ohio Railroad, Thomas Viaduct (1835): Maryland (USA)
Boston & Providence Railroad, Canton Viaduct (1835): Massachusetts (USA)
Balcombe Viaduct (1839): West Sussex, England (UK)
Viaduc de Barentine (1846): France
Ballochmyle Viaduct (1846): Cumnock, Scotland (UK)
Viaduc de Saint-Chamas (1847): France
Chappel Viaduct (1847): Essex, England (UK)
New York & Erie Railroad, Starrucca Viaduct (1848): Lanesboro, Pennsylvania (USA)
(*)Goltzschtal Viaduct (1851): Netschkau vicinity (Germany)
Viaduc de la Bouble (1871): France
Meldon Viaduct (1871, 1879): Okehampton, Devon, England (UK)
Viaduc de Garabit (1885): Saint-Fleur vicinity (France)
New York & Erie Railroad (Bradford Branch), Kinzua Viaduct (1900), Pennsylvania (USA)
Glenfinnian Viaduct (1897): Highland Region, Scotland (UK)
Wüppertal Tramway System (1913): Wüppertal (Germany)
Railway Bridge over Kiel Canal (1913): Rendsburg (Germany)
Lethbridge Viaduct (1909): Alberta (Canada)
Delaware, Lackawanna & Western Railroad, Tunkhannock Viaduct (1915): Nicholson, Pennsylvania (USA)
Union Bridge (1820): Berwick-on-Tweed, England (UK)
Menai Suspension Bridge (1826): Wales (UK)
Conwy Suspension Bridge (1826): Wales (UK)
(*)Szechenyi Bridge (1849, 1915, 1949): Budapest (Hungary)
Tain-Tournon Bridge (1847): France
Delaware & Hudson Canal, Delaware Aqueduct (1849): Lackawaxen, Pennsylvania (USA)
Wheeling Suspension Bridge (1849): West Virginia (USA)
Clifton Suspension Bridge (1864): Bristol, England (UK)
Brooklyn Bridge (1883): New York City (USA)
Pont Rail Gisclard (1909): France11
Acueducto de Tempul (1925): Spain
Eads Bridge (1874): St Louis, Missouri (USA)
(*)Railway Bridge over the Danube between Fetesti and Czernadova (1895): Romania
(*)Mungstener Brücke (1897): Germany
Viaur Viaduc (1902): France
New York Connecting Railroad, Hell Gate Bridge (1917): New York City (USA)
(*)Road bridge over the Rhine (1928): Nijmegen (Netherlands)
Bayonne Bridge (1931): Bayonne, New Jersey (USA)
Sydney Harbour Bridge (1931): Sydney (Australia)
Poughkeepsie Cantilever (1886): Poughkeepsie, New York (USA)
Forth Railway Bridge (1890): Scotland (UK)
Québec Bridge (1917): Canada
Reinforced concrete bridges
Pont de Châtellérault (1900): France
Pennsylvania Railroad, Rockville Bridge (1902): Rockville, Pennsylvania (USA)
Risorgimento Bridge (1911): Rome (Italy)
Royal Tweed Bridge (1928): Berwick-on-Tweed, England (UK)
Plougastel Bridge (1930): Brest (France)
Salginatobel Bridge (1930): Schiers (Switzerland)
Schwandbach Bach Bridge (1933): Schwarzenbach (Switzerland)
Traneberg Bro (1934): Stockholm (Sweden)
(*)Motorway Bridge (1938): Stadtroda (Germany)
Viaducto Ferrioviario Francisco Martín Gil (1942): Spain
Sandö Bro (1942): Sweden
Strömsund Bro (1955): Sweden
Moveable and transporter bridges
(*)Puente de Vizcaya (1891): Portugalete (Spain)12
Martrou Bridge over the Charente: France (nd)
Barton Swing Aqueduct (1893): Eccles, England (UK)
Tower Bridge (1894): London, England (UK)
Middlesbrough Transporter Bridge (1911): England (UK)
Atchison, Topeka & Sante Fe Railroad, Fort Madison Bridge (1927): Fort Madison, Iowa (USA)
Lacey V Murrow Bridge (1940): Seattle, Washington (USA)
Canadian Pacific Railroad, Sault-Sainte-Marie Bridge (1941): Michigan (USA)
- Bridges marked (*) were suggested by Michael Mende.
- The Pont du Gard (France), the Segovia Aqueduct (Spain), and other Roman and Renaissance bridges in the historic centres of Rome, Florence, and Segovia are already on the World Heritage List.
- Primitive bridges, if any survive, may be candidates for World Heritage listing because they illustrate primitive ingenuity and craft technology, which it is important to recognize and preserve.
- The Phra Bhutthos (Cambodia), the Jiangdonggiao (China), the Ponte Saint-Martin (Italy), the Steinerne Brücke (Germany), Pontypridd Bridge (UK), Rumlangsbrücke (Switzerland), the Menai Suspension Bridge (UK), the Puente Ferroviario de Dona Maria Pia (Italy), Strömsund Bro (Sweden), the Pont Rail Gisclard, and Acueducto de Tempul (Spain) were suggested by Professor Shunsuke Baba.
- Stone girder of 76ft (23m) span, total length of bridge 920ft (281m).
- The Ponte Vecchio and the Ponte Santa Trinità form part of the Florence World Heritage site. The Ponte Vecchio replaced a similar bridge that failed in 1333. Some authorities attribute its design to Fra Giovanni da Campi rather than the architect Taddeo Gaddi.
- The Pont Neuf and several other bridges over the Seine form part of the Paris - Banks of the Seine World Heritage site.
- Several collections of cast-iron arches survive in different countries. The largest is in England, there are six in the USA, a few in France, and a remarkable selection in Russia, all of which could be studied as a specific type with the object of possible eventual World Heritage nomination.
- Most of these bridges were designed by Friedrich Wilhelm von Erdmannsdorf and not all are iron. They include the Roman Bridge (1788), the tree-trunk Hornzachenbrücke (1774), the Treppenbrücke, based on the Mathematical Bridge in Cambridge (1773), the Wolfsbrücke (1811), the Chinese Chain Bridge (1781), the Sun Bridge (1796), and the Iron Bridge (1791).
- A case for the world significance of this bridge was made by Stephen Hughes of the Royal Commission on the Ancient and Historical Monuments of Wales.
- This and the Acueducto de Tempul, designed by Albert Gisclard and Eduardo Torroja respectively, are possible candidates for listing as early cable-stayed suspension bridges.
- A suspension ferry (transporter bridge) 525ft (160m) long by 141ft (43m) high.
American Bridge Books
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Smith, H Shirley The World's Great Bridges. Harper & Row, New York, 1965.
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British Bridge Books
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French Bridge Books
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École Nationale des Ponts et Chaussées, No 14, Paris, octobre 1961.
Grattesat, Guy Ponts de France. Presses de l'École Nationale des Ponts et Chaussées, Paris, 1982.
Marrey, Bernard Les ponts modernes: 18e-19e siècles, Picard Éditeur, Paris, 1990.
Mesqui, Jean Le pont en France avant le temps des ingénieurs, Picard, Paris, 1986.
Perronet, J R Description des projets et de la construction des Ponts de Neuilly, de Mantes, d'Orléans, de Louis XVI, etc, de l'Imprimerie de François-Ambroise Didot, Paris, 1788.
Picon, Antoine L'invention de l'ingénieur moderne: l'École des Ponts et Chaussées (1747-1851), Presses de l'École Nationale des Ponts et Chaussées, Paris, 1992.
Polonceau, A R Nouveau système des ponts en fonte, suivi dans la construction du Pont du Carrousel, Carilian-Goeury et Dalmont, Éditeurs, Libraires des Corps Royaux des Ponts et Chaussées et des Mines, Paris, 1839.
Prade, Marcel Les ponts monuments historiques. Brissaud, Poitiers, 1986.
Prade, Marcel Ponts et viaducs au XIX siècle. Brissaud, Poitiers, 1987.
Prade, Marcel Ponts remarquables d'Europe. Brissaud, Poitiers, nd.
Prade, Marcel Les grands ponts du monde: hors de l'Europe. Brissaud, Poitiers, 1992.
German Bridge Books
Boeyng, Ulrich Die ältesten eisernen Brücken der Deutschen Bundesbahn in Baden-Württemberg. Sonderforschungsbereich 315 der Universität Karlsrühe, Karlsrühe, 1988.
Leonhardt, Fritz Brücken, Bridges. The MIT Press, Cambridge, MA, 1984.
Mehrtens, Georg Der deutsche Brücken im 19. Jahrhundert (Reprint of 1900 edition). Düsseldorf, 1984.
Trautz, Martin Eiserne Brücken in Deutschland im 19. Jahrhundert. Düsseldorf, 1991. Wagner, R Die ersten Drahtkabelbruken. Werner- Verlag, Düsseldorf, 1987. & Egermann, R
Wittfoht, Hans Building Bridges: History, Technology, Construction. Beton- Verlag, Düsseldorf, 1984.
Swiss Bridge Books
Bill, Max Robert Maillart. Girsberger, Zürich, 1955.
Killer, Josef Die Werke der Baumeister Grubenmann. Zürich, 1959.
Pottgiesser, Hans Eisenbahnbrücken aus Zwei Jahrhunderten. Basel, 1985.
Italian Bridge Books
Jodice, R L'architettura del ferro, l'Italia. Bulzoni, Roma, 1985.
Siviero, E Il ponte e l'architettura. Città Studi Edizione, Milano, 1995.
Siviero, E, Casucci, Studi e recupero del ponte. Biblioteca di Galileo, Padova, 1995. R, & Gori, R
The author is Chief of the Historic American Engineering Record, National Park Service, US Department of the Interior. He may be contacted at the following address:
Eric DeLony, Historoic American Engineering Record, National Park Service, PO Box 37127, Washington, D.C 20013-7127, USA
© ICOMOS and TICCIH 1996
by Clive Gamble and Chris Stringer
Human origins is a subject of global interest. Not only are there questions of how, when, and where we evolved in the remote past but equally there are those which address the roots of our current ethnic diversity. All of these questions require fossil evidence to be answered. They need material collected from different habitats and samples from many countries. The fossil record has grown enormously in the past fifty years, and in particular with the wealth of finds made in the African Rift valley. It is to be hoped that a similar pace will follow, particularly in other parts of the Old World. We expect that the picture we have today will change enormously in the next fifty years. A brief prehistory of human evolution The course of human evolution can briefly be divided into four periods During this period the hominids split from the last common ancestor. On genetic and anatomical evidence this was a chimpanzee-like primate. Estimates of this divergence put the evolution of a distinct hominid line at 5 million years ago. The early evolution is exclusively African, and most of it south of the Sahara. In the last fifty years many fossil discoveries have revealed a complex picture of contemporary but very different hominids. For example, two million years ago in parts of this region the Australopithecines (southern apes) lived in the same habitats as early examples of our genus Homo. This co-presence of similar but unrelated lineages has been a consistent feature, until the present day, of human evolution. At some time between 2 and 1 million hominids moved north and colonized large parts of Asia and Europe. During this period there are only representatives of the genus Homo. However, there is considerable regional diversity, as shown by the shape of fossil skulls and teeth. These hominids were still confined to parts of the Old World. They were powerfully built and recent finds have shown them to be much larger than previously thought. For much of this period we see the regional evolution of Homo. The best known and largest sample comes from Europe and western Asia, where the Neanderthals form one of the best known fossil populations. As early as 150,000 years ago in eastern Africa we find fossil skulls of essentially modern type. Africa has now been identified both genetically and anatomically as the evolutionary centre for the appearance of people who looked, and eventually acted, like us. The most economical explanation of the evidence is that successive population movements out of Africa replaced the regional populations, such as the Neanderthals, in all parts of the inhabited Old World. One of the novelties associated with these modern people is their global colonization. It is in the last third of this period that people first colonized Australia, the Pacific islands, the northern parts of Asia, the American continents, and the Arctic. This great prehistoric colonization achieved primarily by people with a hunting and gathering lifestyle drew the demographic and geographical map for the later development of ethnic and regional populations of Homo sapiens.
5 million years to 1 million years ago.
1 million to 300,000 years ago.
300,000 to 30,000 years ago.
150,000 - 10,000 years ago.
5 million years to 1 million years ago
1 million to 300,000 years ago
300,000 to 30,000 years ago
150,000 - 10,000 years ago
Human origins is a subject of global interest. Not only are there questions of how, when, and where we evolved in the remote past but equally there are those which address the roots of our current ethnic diversity. All of these questions require fossil evidence to be answered. They need material collected from different habitats and samples from many countries. The fossil record has grown enormously in the past fifty years, and in particular with the wealth of finds made in the African Rift valley. It is to be hoped that a similar pace will follow, particularly in other parts of the Old World. We expect that the picture we have today will change enormously in the next fifty years.
A brief prehistory of human evolution
The course of human evolution can briefly be divided into four periods
During this period the hominids split from the last common ancestor. On genetic and anatomical evidence this was a chimpanzee-like primate. Estimates of this divergence put the evolution of a distinct hominid line at 5 million years ago.
The early evolution is exclusively African, and most of it south of the Sahara. In the last fifty years many fossil discoveries have revealed a complex picture of contemporary but very different hominids. For example, two million years ago in parts of this region the Australopithecines (southern apes) lived in the same habitats as early examples of our genus Homo. This co-presence of similar but unrelated lineages has been a consistent feature, until the present day, of human evolution.
At some time between 2 and 1 million hominids moved north and colonized large parts of Asia and Europe.
During this period there are only representatives of the genus Homo. However, there is considerable regional diversity, as shown by the shape of fossil skulls and teeth. These hominids were still confined to parts of the Old World. They were powerfully built and recent finds have shown them to be much larger than previously thought.
For much of this period we see the regional evolution of Homo. The best known and largest sample comes from Europe and western Asia, where the Neanderthals form one of the best known fossil populations.
As early as 150,000 years ago in eastern Africa we find fossil skulls of essentially modern type. Africa has now been identified both genetically and anatomically as the evolutionary centre for the appearance of people who looked, and eventually acted, like us. The most economical explanation of the evidence is that successive population movements out of Africa replaced the regional populations, such as the Neanderthals, in all parts of the inhabited Old World. One of the novelties associated with these modern people is their global colonization. It is in the last third of this period that people first colonized Australia, the Pacific islands, the northern parts of Asia, the American continents, and the Arctic. This great prehistoric colonization achieved primarily by people with a hunting and gathering lifestyle drew the demographic and geographical map for the later development of ethnic and regional populations of Homo sapiens.
Criteria for selection of hominid sites for inscription
In the light of the current general picture of human and hominid evolution we identify the following six criteria for assessing known sites:
- There is no substitute for good chronologies. Many of the arguments in palaeoanthropology stem from poor dating of fossils. Well dated material allows the taxonomist to sort out phylogenetic relationships and rates of evolutionary change. Dating by isotopic decay methods have revolutionized the subject
- The numbers of fossils from a single locality or within an identifiable geological unit. If well dated, the opportunities for scientific analysis of more than one skull or skeleton are very rewarding. The advantage of large samples lies in tackling questions of population variability, the necessary condition if evolution under natural selection is to occur
- The antiquity of the finds, is also dependent on good dating, preferably by science-based methods. While age is not a sufficient criterion by itself, it must be recognized that finds from certain periods (eg the crucial period 5-4 million years ago when hominids were splitting from the last common ancestor) are still extremely rare
- The potential for further finds must also be recognized. Preservation conditions can be assessed and ranked from poor to exceptional. However, there will always be an element of good fortune in finding fragmentary fossil material. Hominids were never very plentiful and their remains are hard to find. For example, the find of two teeth and a tibia at Boxgrove (southern England) increases in significance because of the preservation of 20km of similar deposits along an ancient shoreline.
- To talk of Hominid sites is increasingly a misnomer. Instead we should think of groups of closely related sites and even landscapes. What is needed in the study of human evolution are good contexts which preserve good environmental and archaeological evidence as well as hominid fossils. This is needed in order to interpret their lifestyles and capabilities.
- A number of fossils have an important historical and even iconic position in the discovery and demonstration of human evolution. These sites, such as Olduvai Gorge and La Chapelle aux Saints, are signposts on the route to our own self-discovery of our evolutionary heritage.
With these points in mind we have drawn up the following provisional list. We have organized the sites into three groups and indicated to which time period (A-D) they belong.
Group 1 Sites with hominid material that are already inscribed on the list Ngorongoro with Olduvai Gorge (Tanzania) A, B Zhoukoudian (China) B, D Awash and Omo Basins (Ethiopia) A, D Willandra Lakes (Australia) D Sangiran (Indonesia) A?, B
Group 2 Sites with hominid remains that score most highly on our six criteria and which we would recommend for consideration
Koobi Fora & Turkana Basin (Kenya) A,C,D Atapuerca (Spain) B Mount Carmel (Israel) C, D Sterkfontein Valley (South Africa) A Hadar/Afar (Ethiopia) A Fossil caves of the Dordogne (France) C, D
Group 3 Sites with important hominid remains for which a good case could be made but which do not score as highly
Eastern Germany travertine sites B, C Dolni Vestonice-Pavlov (Czech Republic) D Murray River cemeteries (Australia) D Solo River (Indonesia) B, C Raised beaches of Sussex (United Kingdom) B
Group 4 Sites with notable fossil material but the lowest scores on the six criteria.
* denotes no fossil hominid finds as yet but with every expectation of discovery.
Shanidar (Iraq) C Klasies River Mouth (South Africa) D *Schöningen (Germany) B Gibraltar (United Kingdom) C, D Monte Circeo (Italy) C, D Grimaldi (Italy) D Elandsfontein (South Africa) B Crimean caves (Ukraine) C, D Kostenki (Russia) D Vogelherd Cave (Germany) D Caune Arago (France) B Croatian caves C, D Haua Fteah (Libya) C, D Niah Caves (Malaysia) D Border Cave (South Africa) D
Recommended general reading
Day, M. H., 1986. Guide to fossil man, 4th edition. London, UK: Cassell.
Gamble, C. S., 1993. Timewalkers: the prehistory of global colonization. Stroud, UK: Alan Sutton.
Oakley, K. P., B.G. Campbell, and T.I. Molleson, 1971. Catalogue of fossil hominids. Part II Europe. London, UK: British Museum (Natural History).
Oakley, K. P., B.G. Campbell, and T.I. Molleson, 1975. Catalogue of fossil hominids. Part III Americas, Asia, Australasia. London, UK: British Museum (Natural History).
Stringer, C., and C. Gamble, 1993. In search of the Neanderthals: solving the puzzle of human origins. London, UK, and New York, USA: Thames and Hudson.
Stringer, C., and E. McKie, 1996. African exodus. London, UK: Cape.
Tattersall, I., 1995. The last Neanderthal: the rise, success, and mysterious extinction of our closest human relatives. New York, USA: Macmillan.
Professor Clive Gamble
University of Southampton,
Professor Chris Stringer
Natural History Museum, London,
14 October 1997
|By Ramón Gutiérrez, Director, CEDODAL
(Centro de Documentación de Arquitectura Latinoamericana, Buenos Aires, Argentina)
LATIN AMERICA is made up of a large group of countries that possess characteristics of cultural identity in common but which at the same time are acknowledged to be very different. They grew up on the ancient pre-Columbian cultures that had developed in Mesoamerica in the north and in the Andean region in the south and were the most part unified under Spanish and Portuguese control in the 16th-19th centuries.
The architectural and urban heritage given special recognition by the UNESCO World Heritage Convention embraces examples from this colonial period, when the different countries were integrated into the organization of the Spanish Empire under several Viceroyalties, or in the case of Brazil as a dependency of Portugal. Whilst Cuba and Puerto Rico remained under Spanish rule until the end of the 19th century, the other countries achieved independence during the first quarter of that century.
An overall criterion that reflects the special cultural characteristics of each of the countries should not fail to consider, as UNESCO already has, the importance of this process of European and indigenous cultural integration that took place during the three centuries of Spanish and Portuguese rule.
However, in a more over-arching perspective the possibility should not be overlooked of incorporating those characteristics developed by the Latin-American countries since achieving their independence in the 19th century, when under the influence of new immigration, internal development, or integration into world commerce they received and assimilated new cultural inputs to their own heritages. This study of the importance of complementing the selection of monuments and sites already inscribed on the World Heritage List is carried out against this background, in order to include the evaluation of single groups that comply with the requirements of excellence and secure protection in the respective countries.
[Note This study was carried out by Dr Gutiérrez in 1997-98 and has been used by ICOMOS in its work as professional advisor to the UNESCO World Heritage Committee since that time.]
These historic centres are without doubt favoured heritage sites, which has resulted in their inscription. However, management of them varies between the different countries, and so it is possible to postulate certain sites within the heritage hierarchy that have not been evaluated effectively, as in the case of the historic centres of Arequipa, Trujillo, Ayacucho, and Cajamarca in Peru or Cuenca in Ecuador. Historic centres need, moreover, a clear preservation strategy on the part of local authorities, the delineation of protection areas, and at the same time the sanction and implementation of preventive measures in order to ensure better stability for these areas. Once historic centres have been declared to be part of the World Heritage there should be a system of monitoring to confirm the continuity of such measures irrespective of periodic political changes at national or local level. The process of increasing population density and urban decay in some of these historic centres that are already on the World Heritage List calls for social and cultural responses that permit the proper use of public open spaces and the recovery of a sizeable heritage that is menaced as a result of a lack of resources on the part of municipalities or national cultural agencies. Strategies for functional regeneration and recycling, the generation of diversifying activities, the encouragement of cultural tourism, and other means of improving the quality of life of the people have made outstanding contributions to the resurgence of historic centres, as can be seen in the case of Quito or more recently in Lima. In other cases urban renewal policies and expulsion of inhabitants can have a serious effect on the heritage, as in the case of Salvador/Bahia (Brazil). Historic centres that are largely made up of 19th century architecture, whether as a result of renewal of the buildings or the creation of new towns, have not so far been recognized by World Heritage inscription. However, they are very clearly typical of some towns of high heritage value, made up of architectural groups from the 18th-20th centuries, as is the case in Buenos Aires or some 19th century towns with substantial evidence of this nature, such as Valparaiso (Chile), Matanzas (Cuba), or Petrópolis (Brazil). It is also important to rescue the urban planning ideas of the 19th century and, in the same way that 20th century thought has been recognized in Brasilia, La Plata (Argentina) should be regarded as a recent urban foundation which drew upon 19th century academic ideas for the layout of diagonal streets, urban parks, and the concept of aesthetic structure in the monumental axes, as well as in the public buildings resulting from an international competition held in 1882. Although UNESCO has recognized several of the towns of this type, such as Guanajuato or Zacatecas (Mexico) or Potosí (Bolivia), these are intermediate towns that have experienced historically a strong continuity for reasons that lie outside their cyclical economic phases. Other mining communities such as Zaruma (Ecuador) and Taxco (Mexico) might be worthy of recognition. Other examples, such as Ouro Preto in Minas Gerais (Brazil), represent smaller towns that relate better to a system of towns integrated by a regional production process and which developed in the same historical period. They are all characterized by a lack of religious houses and by a wealth of parish churches or guilds that typify the mining boom of the 18th and early 19th centuries. In this case it would be sufficient to restrict the criterion for nomination to those towns that maintain high standards of excellence with regard to the heritage and which could also be integrated into a cultural tourism circuit. For example, in the case of Ouro Preto and the Sanctuary of the Bom Jesús at Matozinhos, it would be worth while incorporating Tiradentes, Mariana, and Diamantina. The same applies to the proposed nomination of the Sanctuary of Copacabana (Brazil), where, alongside the undeniable value of the Sanctuary itself, there is the whole policy of creating centres for indigenous converts (reducciones) around Lake Titicaca which resulted in 16th century settlements and high-quality churches, both on the Peruvian side (Juli, Pomata, Zepita, Acora, etc) and on the Bolivian side (Laja, Huaqui, Calamarca, Machaca, Tiahuanaco, etc). It is proposed also to introduce groups of towns that represent forms of settlement connected with trade routes and with the conversion of the Indians. The Indian villages in the Humahuaca gorge and the Calchaquíes valleys (Argentina), those of Chipaya and the Oruro area (Bolivia), the doctrinero villages of Paraguay, or those founded by Bishop Vasco de Quiroga in the Michoacán area (Mexico) provide the possibility of recording these processes of territorial reorganization. There also 19th century village systems, such as those on the Chiloé islands in the far south of Chile or in the coffee-producing area of Colombia, which might facilitate an approach to new forms of settlement, management of production, high-quality local architecture, and individual landscape characteristics. It is necessary to move towards the systematic identification of groups of settlements, even though these may span more than one country (as was done for the Jesuit missions) and consider the possibility of nominating them as groups while at the same time expanding the 19th century base. Although many of the main architectural monuments (Havana, Cartagena de Indias, San Juan de Puerto Rico, Portobelo, etc) are already on the World Heritage List, there is no doubt that they should be visited and understood as forming part of a vast offensive/defensive system which involves not only the great urban fortifications but also places on the coasts and islands, whether under Spanish, English, French, Dutch, or Danish rule. Between the 16th and 18th centuries the Caribbean was a region marked by the struggle for power between the great European nations, who expended vast sums of money in building these fortifications, which in many cases represent the most important heritage investments of a number of towns. For this reason the inscriptions of these architectural monuments should be made as part of a system so as to acknowledge their interaction with one another. Final comments on methodology In this connection the absence of 19th century heritage is very apparent and has required consideration of the recognition needing to be accorded to this cultural period. It is also evident from the tentative lists that it is necessary to identify with accuracy the groups of towns and historic sites that belong to the same system and which have similar value characteristics, so that nominations may be sufficiently broad. Finally, it is advisable that when considering works that are nominally of the 20th century there should be sufficient time elapsed for these to be evaluated in a wider context. The case of the Mexican architect Barragán, whose work has only been recognized in recent decades, illustrates the need for perspective and for not being pressurized by fashionable trends. For this reason it is recommended that architecture inscribed on the World Heritage List should in every case be the work of deceased architects, since this honour should be seen as something other than personal homage, which belongs to another form of recognition than World Heritage listing. At least half a century should elapse after the completion of a building for it to be analysed in a proper perspective in the context of the overall product of the period. Once again, it is necessary to stress that the identification of those ensembles that might be worthy of inscription does not preclude alternative approaches nor does it exhaust the possibilities of what might be considered to be of World Heritage quality. Nor is the presence or absence of adequate provision for legal measures or decision-making at local or national level for the protection and management of this heritage taken account of in this study, which has been based on approaches that are artistic, architectural, urban, cultural, and social, or of the potential for improvement and use of these ensembles. They need to be analysed once each country has undertaken the preparation of the proper measures. What follows has been prepared for each of the countries where outstanding examples have been identified. Among these, various situations have been studied according to the type of heritage and their intrinsic quality. In each country examples from the colonial period are given first, leading up to 19th century cases, where these exist. The lists below contain examples of historic centres, intermediate and small towns, groups of villages, and groups of architectural works treated as systems. Each of these groups obviously includes works from different periods and so they are attributed to the period that predominates within the group. No account is taken in this study of individual architectural monuments. It is thus a list that is indicative in character, aimed at producing a cross-section of the features that may be considered to represent the Latin- American cultural heritage.
T HE CENTRALIZING CONCEPT that began with the creation of the Plaza Mayor as the urban generator from the first third of the 16th century in the creation of Spanish towns served to accumulate official functions and to establish a hierarchy for the central areas of the main towns in the Americas. This is reflected in the appearance, the variations in urban fabric, and the growth of an urban landscape that has been given basic recognition in those inscriptions made on the World Heritage List up to the present.
H ISTORIC TOWNS probably represent one of the most important heritage resources on the American continent. These are generally ancient foundations which were marginalized by urban development processes or reacted to the apogee of finite productive cycles (principally mining) and then fell into decay when their productive resources dried up.
Integrated architectural groups
T HE MOST OUTSTANDING example of this form of territorial evaluation, connected with the encouragement of cultural tourism circuits, which would permit the integrated use of this heritage, is without doubt the fortifications of the Caribbean region.
T HE CENTRAL IDEA behind this new approach firmly ratifies the concepts of quality and excellence that have directed inscriptions on the World Heritage List, but it also seeks to approach these criteria in a form that is representative of the cultural property that characterizes each region, and in particular in the present case the Latin-American continent.
Properties to which priority should be given
These historic centres are without doubt favoured heritage sites, which has resulted in their inscription. However, management of them varies between the different countries, and so it is possible to postulate certain sites within the heritage hierarchy that have not been evaluated effectively, as in the case of the historic centres of Arequipa, Trujillo, Ayacucho, and Cajamarca in Peru or Cuenca in Ecuador.
Historic centres need, moreover, a clear preservation strategy on the part of local authorities, the delineation of protection areas, and at the same time the sanction and implementation of preventive measures in order to ensure better stability for these areas. Once historic centres have been declared to be part of the World Heritage there should be a system of monitoring to confirm the continuity of such measures irrespective of periodic political changes at national or local level.
The process of increasing population density and urban decay in some of these historic centres that are already on the World Heritage List calls for social and cultural responses that permit the proper use of public open spaces and the recovery of a sizeable heritage that is menaced as a result of a lack of resources on the part of municipalities or national cultural agencies.
Strategies for functional regeneration and recycling, the generation of diversifying activities, the encouragement of cultural tourism, and other means of improving the quality of life of the people have made outstanding contributions to the resurgence of historic centres, as can be seen in the case of Quito or more recently in Lima. In other cases urban renewal policies and expulsion of inhabitants can have a serious effect on the heritage, as in the case of Salvador/Bahia (Brazil).
Historic centres that are largely made up of 19th century architecture, whether as a result of renewal of the buildings or the creation of new towns, have not so far been recognized by World Heritage inscription. However, they are very clearly typical of some towns of high heritage value, made up of architectural groups from the 18th-20th centuries, as is the case in Buenos Aires or some 19th century towns with substantial evidence of this nature, such as Valparaiso (Chile), Matanzas (Cuba), or Petrópolis (Brazil).
It is also important to rescue the urban planning ideas of the 19th century and, in the same way that 20th century thought has been recognized in Brasilia, La Plata (Argentina) should be regarded as a recent urban foundation which drew upon 19th century academic ideas for the layout of diagonal streets, urban parks, and the concept of aesthetic structure in the monumental axes, as well as in the public buildings resulting from an international competition held in 1882.
Although UNESCO has recognized several of the towns of this type, such as Guanajuato or Zacatecas (Mexico) or Potosí (Bolivia), these are intermediate towns that have experienced historically a strong continuity for reasons that lie outside their cyclical economic phases. Other mining communities such as Zaruma (Ecuador) and Taxco (Mexico) might be worthy of recognition.
Other examples, such as Ouro Preto in Minas Gerais (Brazil), represent smaller towns that relate better to a system of towns integrated by a regional production process and which developed in the same historical period. They are all characterized by a lack of religious houses and by a wealth of parish churches or guilds that typify the mining boom of the 18th and early 19th centuries.
In this case it would be sufficient to restrict the criterion for nomination to those towns that maintain high standards of excellence with regard to the heritage and which could also be integrated into a cultural tourism circuit. For example, in the case of Ouro Preto and the Sanctuary of the Bom Jesús at Matozinhos, it would be worth while incorporating Tiradentes, Mariana, and Diamantina.
The same applies to the proposed nomination of the Sanctuary of Copacabana (Brazil), where, alongside the undeniable value of the Sanctuary itself, there is the whole policy of creating centres for indigenous converts (reducciones) around Lake Titicaca which resulted in 16th century settlements and high-quality churches, both on the Peruvian side (Juli, Pomata, Zepita, Acora, etc) and on the Bolivian side (Laja, Huaqui, Calamarca, Machaca, Tiahuanaco, etc).
It is proposed also to introduce groups of towns that represent forms of settlement connected with trade routes and with the conversion of the Indians. The Indian villages in the Humahuaca gorge and the Calchaquíes valleys (Argentina), those of Chipaya and the Oruro area (Bolivia), the doctrinero villages of Paraguay, or those founded by Bishop Vasco de Quiroga in the Michoacán area (Mexico) provide the possibility of recording these processes of territorial reorganization.
There also 19th century village systems, such as those on the Chiloé islands in the far south of Chile or in the coffee-producing area of Colombia, which might facilitate an approach to new forms of settlement, management of production, high-quality local architecture, and individual landscape characteristics.
It is necessary to move towards the systematic identification of groups of settlements, even though these may span more than one country (as was done for the Jesuit missions) and consider the possibility of nominating them as groups while at the same time expanding the 19th century base.
Although many of the main architectural monuments (Havana, Cartagena de Indias, San Juan de Puerto Rico, Portobelo, etc) are already on the World Heritage List, there is no doubt that they should be visited and understood as forming part of a vast offensive/defensive system which involves not only the great urban fortifications but also places on the coasts and islands, whether under Spanish, English, French, Dutch, or Danish rule.
Between the 16th and 18th centuries the Caribbean was a region marked by the struggle for power between the great European nations, who expended vast sums of money in building these fortifications, which in many cases represent the most important heritage investments of a number of towns. For this reason the inscriptions of these architectural monuments should be made as part of a system so as to acknowledge their interaction with one another.
Final comments on methodology
In this connection the absence of 19th century heritage is very apparent and has required consideration of the recognition needing to be accorded to this cultural period. It is also evident from the tentative lists that it is necessary to identify with accuracy the groups of towns and historic sites that belong to the same system and which have similar value characteristics, so that nominations may be sufficiently broad.
Finally, it is advisable that when considering works that are nominally of the 20th century there should be sufficient time elapsed for these to be evaluated in a wider context. The case of the Mexican architect Barragán, whose work has only been recognized in recent decades, illustrates the need for perspective and for not being pressurized by fashionable trends.
For this reason it is recommended that architecture inscribed on the World Heritage List should in every case be the work of deceased architects, since this honour should be seen as something other than personal homage, which belongs to another form of recognition than World Heritage listing. At least half a century should elapse after the completion of a building for it to be analysed in a proper perspective in the context of the overall product of the period.
Once again, it is necessary to stress that the identification of those ensembles that might be worthy of inscription does not preclude alternative approaches nor does it exhaust the possibilities of what might be considered to be of World Heritage quality. Nor is the presence or absence of adequate provision for legal measures or decision-making at local or national level for the protection and management of this heritage taken account of in this study, which has been based on approaches that are artistic, architectural, urban, cultural, and social, or of the potential for improvement and use of these ensembles. They need to be analysed once each country has undertaken the preparation of the proper measures.
What follows has been prepared for each of the countries where outstanding examples have been identified. Among these, various situations have been studied according to the type of heritage and their intrinsic quality. In each country examples from the colonial period are given first, leading up to 19th century cases, where these exist.
The lists below contain examples of historic centres, intermediate and small towns, groups of villages, and groups of architectural works treated as systems. Each of these groups obviously includes works from different periods and so they are attributed to the period that predominates within the group. No account is taken in this study of individual architectural monuments. It is thus a list that is indicative in character, aimed at producing a cross-section of the features that may be considered to represent the Latin- American cultural heritage.
A R G E N T I N A
|1||The towns of La Quebrada de Humahuaca and Puna Jujena (Province of Jujuy)|
This is a group of towns which grew out of the old encomiendas (estates) of the 16th and 17th centuries and the miners' settlements of the former Tojo Marquisate. These towns, which are located in the extreme north-west part of Argentina, close to the Bolivian border, are within two clearly delineated geographical zones, the Humahuaca pass and the Jujena puna (high plateau).
Most of these villages have considerable architectural unity resulting from slow consolidation and growth. In all of them, the church is the focal point from both the urban and the architectural standpoint. The church provides the basic configuration of several of these villages, among them San Francisco de Yavi and Purmamarca, both of which were built in the 17th century and are listed national historical monuments. The same can be said of many of the 18th century churches, some of which received additions or were modified in the 19th century. Among them are Humahuaca, Uquia, Huacalera, Tilcara, Tumbaya and Tafna, along the road leading from Upper Peru (today Bolivia) to Río de la Plata.
The chapels and villages of Coranzuli, Susques, Casabindo, and Cochinoca provide an idea of the scale of the stretches of land occupied on the Jujena high plateau. All of these places of worship have unique features, ranging from their atria with posas (small chapels used during processions) to artistic treasures of paintings and religious imagery. Some of the wall paintings are of particular interest.
The entire group may be appreciated for its qualities in terms of heritage, and also in terms of its location and the way it fits in with the landscape. Nearly all these chapels are protected as a result of their status as listed historic monuments, and the majority have been restored recently.
|2||The Jesuit estancias (Province of Córdoba)|
The Jesuits established an effective economic system in the central region of Argentina to provide for their schools, university, and novitiate. These estancias included churches built in the 17th and 18th centuries, together with living quarters and other buildings. A number of these estancias, such as Alta Gracia, comprised a large reservoir and dwellings which later on would be occupied by Virrey Liniers. Adjacent to the Jesús María estancia is an interesting 18th century postal building known as the Sinsacate Post Office.
The most isolated and probably the oldest is the Candaleria estancia, while the Santa Catalina estancia is the largest. The Caroya estancia, which was the last one built in the 18th century, was used for the manufacture of guns during the War of Independence.
The churches and cloisters house some noteworthy examples of religious imagery. Worthy of mention are those in the Jesús María Museum, at the estancia of the same name. All the buildings referred to are listed historic monuments and as such benefit from special protective measures. As in the preceding case, the value of the entire group of estancias exceeds the individual value of each taken separately.
INSCRIBED ON THE WORLD HERITAGE LIST IN 2000
|3||The villages of the Calchaquies Valleys (Province of Salta)|
Although they were founded in the 17th and 18th centuries, a substantial number of these villages underwent further growth and changes in the first half of the 19th century. Set in a spectacular landscape, the villages were dependent upon haciendas (country estates) or encomiendas(concessions). The oldest village in the group, San Pedro Nolasco de Molinos, is no exception. The chapels at these estates and the oratories at various locations along the roads were focal points for these villages, which are characterized by geographical and functional unity.
The villages of Cachi, Seclantás, Angastaco, San Carlos, and at a later date Cafayate are the embodiment of a strategy of land acquisition to the detriment of the Calchaquí Indians, who had long been settled in the area. The bitter conflicts lasted well into the 17th century.
The value of this rich heritage of both civil and religious architecture, comprising houses, haciendas, oratories, and churches, has been recognized by the Argentine Government by designation as a National Monument. At the present time 19th century vernacular architecture plays a dominant role, a number of buildings and large houses having been restored for the purpose of tourism.
|4||The town of La Plata (Province of Buenos Aires)|
La Plata was laid out in 1882 when Buenos Aires became the Federal Capital of Argentina. It was seen as the model for the new administrative city. Together with his architects, the most talented of whom were Juan Martín Burgos and Pedro Benoit, the Governor, Dardo Rocha, who spearheaded this urban project, worked with the aim of building a modern city in accordance with the latest criteria of European town planning. They accordingly made use of a structure comprising wide thoroughfares, monumental buildings, and diagonal avenues leading to public open spaces and small squares of various sizes. The town planning focused on geometrical principles and urban beauty, in the form of parks, the road connecting with the port, and the peripheral avenues.
The city grew rapidly but nevertheless was able until recent years to maintain the urban qualities incorporated into its original plan. An international architectural contest was organized for the design of the public buildings, most of which were in the event designed by German and Argentine architects. The buildings most worthy of note are the Municipal Palace, the House of the Government, the Parliament Building, the Museum, the Observatory, the Railway Station, the Pasaje Rocha, and the Cathedral.
The plan of La Plata, which was considered to represent a major breakthrough, exerted a considerable influence all over the continent. Some examples are the layout of Belo Horizonte (1897) in Brazil and the opening up of diagonal avenues in large capital cities such as Buenos Aires, Rio de Janeiro, and Montevideo. This is unquestionably the most significant 19th century urban plan anywhere in Latin America, and as such deserves the same recognition as that given by the World Heritage Committee to Brasilia for the 20th century.
|5||The monumental centre of Buenos Aires|
Known as the most European city in America, Buenos Aires, although founded in 1580, has only retained a handful of churches from the colonial period. It does, however, boast magnificent 19th century architecture, with buildings on a par with the most distinguished achievements of the Old World.
The construction in 1890 of the Avenida de Mayo, which opened up a wide boulevard on the same axis as the old Plaza Major of the city, was instrumental in defining the urban profile of this central part of the city, which coexists with the old colonial quarters in the southern part, now replaced by 19th century architecture which is considered to be the historic centre of Buenos Aires. It is necessary to consider the city with its 19th century monumental heritage which, though spread over a vast area, nonetheless depicts a series of large ensembles that together make up the city's image. Within this heritage one must recognize the integration of industrial architecture and that of the port. The embankments of Puerto Madero, which have been rehabilitated for use by service industries, exemplify this integration.
There are in fact few cities in Latin-America with such high- quality examples of 19th century architecture together with a large number of churches, most of which are from the 18th century.
The Avenida de Mayo, which runs over the continent's first underground railway line (1913), and many more outstanding buildings in the city are protected by the historic monuments legislation or by municipal ordinances. In some cases restoration or maintenance works have been carried out.
B O L I V I A
Of the various groups of monuments on the tentative list, the Copacabana Sanctuary and the community of Chipayas are worthy of consideration. However, these properties should be integrated within regional groupings of special value.
|1||The Copacabana Sanctuary and the region of Lake Titicaca (Bolivia and Peru)|
This is one of the most important areas of settlement, dating back to the 16th century, where there is also evidence of the presence of indigenous cultures, such as those of Tiahuanaco and the Lupacas as well as the Incas. Despite its outstanding character, the Copacabana Sanctuary forms an integral part of a system of diocesan villages which took shape around the shores of Lake Titicaca.
The towns of Carabuco, Calamarca, Machaca, Viacha, Tiahuanaco, Huaqui, and Laja in Bolivia provide churches and other examples of vernacular architecture of outstanding architectural and artistic value. Equally, on the Peruvian side in the vicinity of Chucuito, the churches of Juli, Pomata, Paucarcolla, Llava, Acora Zepita, Puno, Ayaviri, Asillo, Lampa, Umachiri, Oruillo, and elsewhere, built between the 16th and 18th centuries, are of noteworthy quality. Their mural paintings, sculptures, furniture, and silver ornaments all bear witness to the region's heritage of exceptional expressiveness. In addition to all these elements there are also many archaeological sites, such as the Chulpas de Sillustani.
It is recommended that this entire ensemble should be considered as a whole, in so far as it reflects the historical development of the area and the common history of the various elements. It would not seem logical to designate Copacabana on its own, thus setting aside, for instance, the four splendid churches in the village of Juli.
|2||Chipayas and the Oruro region|
Although the Chipayas settlements possess some peculiarities in terms of the configuration of the houses and the structure of the town itself, they nonetheless have a structural relationship with other settlements in the same region of Bolivia. This applies to the towns of Caquiaviri, Corque, Curahuara de Caragas, Paria, Ancocala, Yarvicolla, Sepulturas, Totora and many others dating back to the end of the 16th century during the period of the reducción, when Indian villages were created by the Spanish missionaries to convert the Indian population to Christianity. These villages have kept their characteristic layout comprising the square, the church and its atrium, and small posa chapels.
Any nomination should include all these monuments which together give the area its special character. Special attention should be given to the quality of these various properties, which include wall paintings and religious ornamental objects.
B R A Z I L
It is considered to have been a mistake not to have included the city of Alcantara in the nomination of São Luis do Maranhão, since these two cities are located adjacent to one another.
|1||All the towns of Minas Gerais|
Ouro Preto and the Sanctuary of Bom Jesús de Matozinhos have already been inscribed on the World Heritage List. There is a case to be made for extending this, to include the towns of Tiradentes, Mariana, Diamantina, San João de Rey, and Sabará, which together form important ensembles from the 18th and 19th centuries that are worthy of forming part of a serial inscription, because of their specific form of land occupation and the mining activity of this region. Furthermore, these villages include monuments and outstanding architectural and artistic heritage which are the object of an in-depth maintenance and restoration campaign by the National Department for Historical and Artistic Heritage (SPHAN). There is also very well integrated architecture and the links with the surrounding landscape and environment are of high quality.
|2||The city of Pétropolis|
This is another interesting urban unit built in the 19th century (1840), centred on the Imperial Palace, the residence of the only European royal family to have settled in South America. The layout of the town conforms organically to the topography, reflecting the traditions of Portuguese town planning in its ability to fit in well with the landscape (even though the town was laid out by a German, Julius Koeller).
The academic architecture of Pétropolis, which includes a number of structures of historical interest, makes it a town that is of interest in terms both of its mid-19th century construction and of its specific urban functions. Pétropolis could be nominated as a further example of the type of urban layout already identified in the case of La Plata (Argentina) and also to be found in other 19th century cities, such as Valparaiso (Chile).
C H I L E
|1||The chapel and towns of the Chiloe Islands (Southern Chile)|
This is a large series of churches, most of which are of wooden construction and which the Jesuits began building in the 18th century, although the great majority were constructed in the 19th century.
The Jesuits applied the concept of itinerant missions, which on certain of the small islands of the archipelago took the form of a number of chapels around which hamlets had to be built. The centre of evangelization was the Colegio located in the town of Castro. Following the expulsion of the Jesuits in 1767, most of these chapels were taken over by members of the Franciscan order of Propaganda Fide, which continued the established practice of itinerant missions.
There are several dozen of these churches, from the old church of Achao to the 19th century Castro Cathedral. They illustrate wood construction techniques and high-quality solutions for the use of space and are unique specimens within the context of architecture in the Americas. Among them, those of Rilán, Dalcahue, Nercón, Quinchao, Chonchi, and Vilipulli are particularly worthy of note.
In recent years the painstaking restoration and maintenance of the chapels by a group of architects with private backing has made it possible to improve the conservation of this heritage substantially.
THE CHURCHES OF CHILOE WERE INSCRIBED ON THE WORLD HERITAGE LIST IN 2000
|2||The historic centre of Valparaiso|
Valparaiso, the largest port in Chile and the present seat of the Parliament, was founded in the 16th century but only grew slowly until well into the 18th century. It is, moreover, one of the cities in which the architectural heritage of the 19th century is the best expressed anywhere on the continent.
The squares of the city (Matriz, Municipalidad, and Aduana) make up, together with the area of the port, a sequence of highly interesting spaces brimming with vitality. The urban grid is also an important element which has endured over time.
At a time when further construction seems to have reached a standstill in many countries of the American continent, due to a lack of resources arising from long wars and internal strife, Valparaiso succeeded in consolidating its position as a city of classic architectural design, built according to a model characterized by the influence of the burgeoning Anglo- Saxon population, which has left an indelible mark here. In the first place, this architecture is distinct from its counterparts, inspired by French and Italian academicism, in many of the cities of the Southern Cone, expressing itself by means of the use of wood and metal cladding in the context of very original solutions.
The situation of the city, along a narrow coastal strip, made it necessary to build on the steep topography of the cerros, resulting in a spectacular cityscape. This has given the city some breathtaking panoramas in a number of areas.
In terms of both the value of its architecture and that of its atmosphere and the cityscapes that it provides, Valparaiso, along with La Plata, Buenos Aires, and Pétropolis, composes the most significant collection of 19th century urban architecture in South America, spanning its various nuances and periods.
C O L O M B I A
|1||The historic town centre of Tunja|
Although in recent years the centre of Tunja has fallen victim to construction work without proper control measures, this town nonetheless conserves the only surviving 16th houses in South America, as well as a very interesting Plaza Mayor (Central Town Square).
Along with a number of important churches from the 16th to 18th centuries, such as the Cathedral, the Churches of Santa Bárbara, Santa Clara, Santo Domingo (with its Chapel of the Rosario), San Ignacio, San Agustín, San Lázaro, El Topo, and San Francisco, the houses of Rendón el Fundador and that of Escribano Vargas with its magnificent mural paintings constitute an outstanding artistic heritage.
These churches and houses, which are protected as Historic Monuments, have in the past ten years undergone maintenance and restoration work (including the mural paintings) and in general are in very good condition.
|2||The historic town centre of Santa Fe de Antioquoia|
This is another example of an intermediate-sized city possessing a high-quality and relatively homogeneous regional architecture with buildings of a monumental character, among them the late 18th century Cathedral and the old Jesuit Church of Santa Bárbara.
Santa Fe de Antioquia was founded in 1546 and its subsequent development was very slow until the 18th century, when it became a major commercial centre in the region. The buildings constructed during these periods, which include a number of very interesting large houses, have since 1959 been protected by legislation (the Organic Law for the Colonial Monuments of Colombia). However, there is need for there to be some amendments to the urban ordinances. To this end, a number of different studies have been conducted by academic specialists.
The homogeneous nature of the city centre and the high quality of the urban landmarks are such that it is recommended that Santa Fe de Antioquia be considered for inclusion on the List.
|3||Villages of the coffee-producing area (Antioquia and Caldas)|
The small towns in these regions of Colombia resulted from 19th century colonization. They are characterized by domestic architecture that makes use of highly detailed carved wood.
A number of these towns, such as Jericó, have both a Franciscan and a Claretian church. Titiribi with its Girardot Circus-Theatre and the large complexes of Salamina and Aguadas have been declared National Historic Monuments.
To this list might also be added the towns of Jardín, Montenegro (with its National Coffee Museum), Venecia, Santa Rosa de Osos and Armería, whose inhabitants are fully aware of the value of the towns in which they live.
In this way it would be possible to pay tribute to one of the principal processes of colonization, based on coffee production. This would establish a very clear relationship between the respective functions of the urban and rural settlements, which bear witness to the establishment of a territory and its source of economic wealth. This architecture with its vernacular features equally reflects refinements in execution and a sense of integration which make it truly unique anywhere in the Americas.
C U B A
|1||The historic centre of Camagüey|
Camagüey is one of the towns of the island of Cuba which in recent years has received the greatest attention from that country's agency for the Architectural and Urban Heritage.
Camagüey has undergone significant modifications on three occasions since it was founded in the 16th century under the name of Santa María del Puerto Principe. It does not conform with the traditional Hispanic quadrilateral urban layout, but rather has been more spontaneous in its formation, thereby clearly setting itself apart from other towns. An pattern of narrow streets developed here linking open spaces with the various urban landmarks, such as churches, convents, and hospitals which in turn give a structure to the quarters of this historic town centre, one of the largest in Cuba.
The historic centre comprises a series of 18th century monuments, among which of particular interest are the churches of La Matriz, San Juan de Dios (including a hospital), La Merced, La Soledad, and Santo Cristo del Buen Viaja. The church of Santa Ana dates back to the 17th century and those of San Lázaro and El Carmen were built in the 19th century. Nearly half the buildings in the central part of Camagüey date from the 18th and 19th centuries, and this accounts for the visual impact of its homogeneous cityscape, which includes high-quality colonial houses.
|2||The historic centre of Matanzas|
The city of Matanzas has one of the most interesting 19th century historic centres anywhere in the region. It should be pointed out that Cuba remained under Spanish control until 1898, and so the buildings here reflect a neo-classicism directly linked with the buildings constructed in Spain until the end of the 19th century.
The Teatro Sauto, the various residences, the churches, and the notable 19th century Botica (Pharmacy), along with the streets and small squares, give Matanzas a unique urban expression which is a living tribute to the romantic iconography of the 19th century.
The social and economic reality of the island is nevertheless such that new types of solution must be found to protect this town. Its architectural heritage is of a rare quality, finding expression both in the typology of the houses with stained glass windows and the adjoining grillwork and in the environmental improvement of the part of the town built facing the river.
Matanzas is yet another example of a 19th century historic town centre deserving of this distinction in order to secure the continuity of a strategy for preservation and environmental control, the various social measures for which still remain pending.
|3||The group of fortifications in the Caribbean region|
Although this proposal has already been put forward at the meeting held in Cartagena de Indias (Colombia) in 1996, a number of separate nominations have also been made by States Parties to the Convention for individual components of this system. It is repeated here under the heading of Cuba because some of the fortifications in Havana are already on the List and those in Santiago de Cuba are currently under consideration.
It would be advisable to adopt an overall approach to these defensive/offensive systems, which include a number of sites already on the List (Portobelo, Cartagena de Indias, Havana, Santo Domingo, etc). Such an approach would include properties in a number of former Spanish colonies and also English, French, and Dutch colonies. To this end, the studies compiled by CARIMOS and the OAS, as well as Ramón Paolini's book Fortificaciones del Caribe, illustrate the location and the quality of these fortifications dating from the 16th to the 19th centuries.
E C U A D O R
|1||The town of Zaruma|
Zaruma came into being as a mining town in the 16th century and grew considerably as a result of the production of the mines. It is located on rugged terrain and has grown in an organic way, resulting in high-quality townscapes. The greater part of the town was renovated in the 19th century. The growth of agriculture in the region in the 17th century consolidated this mining town and gave rise to a boom period which drew to a close in the 18th century. However, this changed in the late 19th century, when Zaruma Gold and later the South American Development Company established operations here, initiating the renewal of the town.
The relationship between the town and the surrounding landscape, coupled with its isolation, have enabled the town to retain its homogeneous appearance and to be recognized for its historic and cultural expression. In view of the continuous mining activity, now in decline, and a 16th century urban fabric and townscape that were modified in the 19th century, Zaruma can justly be considered as an important example of historical events viewed within the broader Latin American context.
|2||The historic centre of Cuenca|
Cuenca was founded in 1557 on the former site of the Inca settlement of Tomebamba and is today a good-sized town in the mountains of Ecuador. The Plaza Mayor and the Plaza de San Francisco are public spaces which still contain important architectural monuments such as the old Matrizand a number of churches. The enclosed Conception Monastery has preserved a rich artistic heritage, including 18th century wall paintings. Cuenca has retained its homogeneous vernacular architecture, making use of indigenous materials and the techniques appropriate to them.
These factors resulted in 1982 in the National Institute for Cultural Heritage in Ecuador protecting the historic centre of Cuenca by establishing the concept of archaeological areas (Todos Santos), the special area, with primary protection areas and buffer zones.
The conservation of the magnificent area of natural landscape of the Barranco (steep valley) of the Tomebamba River and the restoration of the Casa de Chaguarchimbana undertaken recently provide evidence of this growing concern for the heritage of Cuenca.
INSCRIBED ON THE WORLD HERITAGE LIST IN 1999
G U A T E M A L A
|1||The town of Chichicastenango|
Amongst the many indigenous towns of Guatemala which reflect the process of organization of colonial space, Chichicastenango additionally embodies a number of specific factors, such as traditions which have endured, a large Sunday market, the lively character of the sanctuary, and an incomparable architectural and urban heritage.
The 18th century church of Chichicastenango century has retained its elevated atrium and the posas (small chapels) in the corners of the open square, ie the pristine structure of the Indian village. The popular architecture here consists of homogeneous spaces where the vitality of the indigenous people reflects both a strong feeling of the present and a deeply rooted historical and cultural heritage.
M E X I C O
|1||Patzcuaro and the villages of Michoacan|
The villages founded in the 16th century by Bishop Vasco de Quiroga in the Michoacan region together make up one of the most important social and cultural experiments anywhere in the Spanish colonies of the Americas. Taking his inspiration from the principles set out by Thomas More in his Utopia, Vasco de Quiroga created a series of hospital-villages (guataperas) to protect the indigenous people from the greed of his own compatriots, making sure that the various communities specialized in different manual trades.
From his episcopal see in Patzcuaro, the Bishop laid out a noteworthy urban design that integrated small squares and public spaces, and sought to build his Cathedral at the centre along the lines of the ideal cities of Renaissance humanism.
Other towns such as Tzin-Tzun-Tzan ("Place of the Humming Birds") still have their 16th century churches with open chapels, accommodation for converts undergoing instruction, and other open spaces which bear witness to the extent of this experiment. Uruapan and Tiripetío, with their churches covered with wall paintings, Chapitiro, Tócuaro, Uricho, Santa Fe de la Laguna, Paracho, Santa Clara, Jaracuiro, etc provide a significant understanding of the regional breadth of this unique project, comparable with the Jesuit missions of Paraguay in their social and cultural aspects.
|2||The historic centre of Tlaxcala and the Sanctuary of Ocotlan|
Tlaxcala is a town in which a number of important 16th century monuments, including the Casas Reales, the Cathedral, and the Church of San Francisco with its distinctive mudéjar wooden ceiling, have survived. Its public spaces and other groups of monuments, such as the Palacio de Justicia (courthouse), make this town near Puebla a reference point in terms of Mexican architectural and urban heritage.
The Sanctuary of Ocotlan, located near Tlaxcala, is a masterpiece of the Mexican Baroque style. It was built in the 18th century and its red ceramic-covered towers stand out in stark contrast to the well proportioned white facade. Inside, the alcove of the Virgin is one of the finest examples of Baroque anywhere in the region.
The town and the Sanctuary are outstanding representatives of two great periods of Mexican architecture, the 16th and 18th centuries.
|3||San Miguel de Allende|
This historic centre is composed of high-quality buildings from the 18th and 19th centuries equal to those in Zacatecas or Guanajuato. Of particular note is the siting of this city, founded in 1542, in relation to its surrounding landscape. Many of the superb houses in this town are now in use for tourism. Among the most distinguished monuments are the homes of Ignacio Allende and the Counts of the Canal. Among the outstanding churches are those of San Francisco, Nuestra Señora de la Salud, the Oratory of San Felipe Neri, and the Santa Casa de Loreto, all built in the 18th century, and the 19th century Iglesia Parroquial (Parish Church).
The mining town of Taxco, which was founded in the 16th century, nowadays receives many tourists. Its location on uneven, rugged terrain and the spontaneous nature of the layout of the city has resulted in a highly picturesque settlement, even though in some areas of the town the houses are more often "seen from the rear." Among its monuments are the Church of Santa Prisca (1748-54), one of the foremost examples of Mexican Baroque architecture, which overlooks the town from its site perched on top of a hill in the centre of the town, making it a prominent monumental landmark.
The narrow streets of Taxco, its market places and its streets with stairways or ramps are all elements which, with their different spaces, contribute to the making of an urban atmosphere which is both pleasant and full of surprises and discovery. The residences of José de la Borda (Palacio Municipal) and the house of the painter Figueroa (now a museum) both date from the 18th century. Their interest is comparable with that of the house where Humbodlt lived in 1803, at present a store where local art and craftwork are sold.
P A R A G U A Y
Although Paraguay has begun taking steps to nominate the Carlos Antonio Railway Line to the World Heritage List, this is considered to be of far less interest than the groups of doctrinero villages. It is also felt that several more of the Jesuit mission villages should be added to the List.
|1||The Jesuit missions|
The missions of Trinidad and Jesús have already been included on the World Heritage List. In spite of some unfortunate work that has been carried out on it, the whole of San Cosme and Damián, which has kept its Colegio, should be included, as well as a part of what the Jesuits were able to complete before being expelled in 1767.
The villages of Santa Rosa should also be included. Here, with some minor modifications, the houses of the Indians, the Chapel of Loreto, and the remains of the tower as well as retablos and high-quality religious images still remain. The finest collections of Jesuit religious imagery are to be found in the villages of San Ignacio Guazú and Santa María de Fe; the Museum of the Missions is in the former. These missions should be included on the List in virtue of the fact that they form a unit.
|2||The doctrinero villages|
Not long after the city of Asunción was founded in 1537, a series of villages was created where the Christian doctrine was taught to the Indians of the estate by the Franciscans, who began evangelizing in the region. These villages, which were later handed over to secular clerics, are highly interesting examples of wooden architecture. A unique aspect of these settlements is that their churches are set in the middle of the main squares and not on one of the sides.
Most of the churches were rebuilt in the course of the 18th century using the same techniques of construction, and so in the villages there is a series of colonnaded churches and in some cases houses with wooden galleries in front, which deserve to be considered as a unique regional architectural solution. Among the most noteworthy churches are those of Yaguarón, Capiatá, Piribebuy, Valenzuela, Paraguarí, and Emboscada, the last-named founded in 1740 by former black slaves who were freed to serve as a defence militia against the warlike threats of the indigenous peoples. The architectural features of these various buildings are not simply limited to the internal (the church as a place of assembly) or external use of space, but also include artistic creation in the form of exceptional retablos and polychrome religious images.
P E R U
|1||The historic centre of Arequipa|
Located in the southern part of Peru and founded in 1540, Arequipa is one of the most interesting examples of architecture and urban planning in Latin America. It is possible here to identify the site of the ancient indigenous settlement, the grid of the Spanish town, and the reducciones(townships established subsequently for Indians converted to Christianity) of Yanahuara and Cayma which, though located on the other side of the river, now form part of the town itself.
The architecture of Arequipa displays some of the earliest examples of the mestizo Baroque style, to be found on the facade of the Compañia de Jesús (1698) and in the churches of Santo Domingo, La Merced, Santa Teresa, Santa Rosa, the Third Order of San Francisco, and other 18th century buildings. The monastery of Santa Catalina of Siena, which was opened to the public some ten years ago, is a prime example of a town within a town where the nuns lived in small "houses" or cells laid out along narrow inner streets behind a high wall.
The 18th century houses that remain in Arequipa are unique in their use of a local volcanic stone for construction. The indigenous character of these houses is shown by their large doors and windows. The houses of Tristán del Pozo, Moral, Iriberri, La Moneda (the Mint), etc embody first-class civil architecture.
The earthquakes of 1784 and 1868 had an effect upon the heritage of Arequipa in that they led to the birth of a classical architecture of high quality that integrated with the earlier Baroque buildings. The Cathedral, rebuilt following destruction by fire in 1844, is another important monument, the location of which on the arcaded Plaza de Armas is significant from a scenic point of view.
In Peru, historic monuments are protected by national legislation, and at present efforts are being made to improve the provisions for the protection of the historic part of Arequipa.
INSCRIBED ON THE WORLD HERITAGE LIST IN 2000
|2||The historic part of Trujillo|
Located in the northern coastal region of Peru, near the pre- Inca citadel of Chan Chan, which is one of the most interesting archaeological sites anywhere in the country and is inscribed on the World Heritage List, the town of Trujillo, founded in 1534, developed in a somewhat curious way owing to the oval layout of its late 17th century walls, the work of the Italian engineer Formento.
Trujillo has retained a large part of its colonial architectural heritage, especially that created during its apogee in the 18th century, when the Cathedral and the churches of San Francisco, El Carmen, Santo Domingo, La Merced, Santa Ana, Santa Clara, Belén, and the interior of the Church of San Agustín were built. On a par are the handsome 18th and 19th century mansions, which contribute to the homogeneity of the historic town centre of Trujillo. Large doors and patios, remarkable windows with extensive iron grilles, and buttresses and vestibules with mural paintings (which can also be seen here and there on the facades) make a number of houses stand out, among them those of Ganoza, the Marquis of Herrera and Valle, Urquiaga, and Marshal Orbegoso.
In recent years the historic centre has been the focus of restoration and improvement work, which has included the extensive use of colour in the area of the Plaza Mayor and on a number of the monuments.
Any proposal for the inscription of Trujillo on the World Heritage List should include the archaeological sites nearby.
|3||The historic centre of Ayacucho|
Ayacucho was founded around 1540 under the name of Huamanga; its present-day name comes from the battle that took place at a place nearby with this name, which gave Peru its independence and brought Spanish rule in South America to an end.
One of the peculiarities of the colonial architecture of Ayacucho, where 18th century buildings predominate, is undoubtedly the spacious nature of its houses and patios, along with the highly varied styles of its churches. The main residences - those of Garcia del Barco, the Marquis of Totora, the so-called "La Tres Máscaras" (The Three Masks), Ruiz de Ochoa, and the Marquis of Cabrera - are all of high quality. Among the religious buildings, the church of Santo Domingo with its open chapel in front, the late 17th century Cathedral, the Church of the Jesuits and its Colegio (the seat of the University), the churches of Buena Muerte, San Francisco de Paula, San Francisco de Asís, Santa Ana and Santa Clara, Santa Teresa with its magnificent mudéjar retablo, and the church of La Merced are all highly prized elements of the heritage which deserve to be given similar recognition to that accorded to those historic centres that are already on the List.
|4||The historic centre of Cajamarca|
The historic conquest of Peru which marked the fall of Atahualpa and the triumph of Francisco Pizarro was completed at the Inca city of Cajamarca. It was here that the Spaniards founded their new city, establishing a new urban profile but still keeping the historic centre, known as the Cuarto de Rescate (the Redemption Quarter).
The main buildings in this historical centre date from the 17th and 18th centuries, with churches rising above a series of sober and homogeneous houses with remarkable facades and craftsmanship in wood by local artisans. The Cathedral, with its interesting stone bosses, the Church of San Francisco, which is purported to be the oldest in the town, and the hospitals of Belén and La Recoleta give an idea of the high quality of the monumental works here, which deserve recognition as exceptional heritage in an intermediate-sized town.
|ANNEX II||Analysis of the World Heritage List and national tentative lists|
As a preparatory step in preparing the main report above, an analysis was made of properties inscribed on the World Heritage List, those included in tentative lists submitted by Latin-American States Parties to the Convention, and others considered to be worthy of consideration. This is presented below in tabular form.
Two points needs to be emphasized with regard to this table. First, it represents the initial approach to the study, the definitive recommendations of which are given in the main text above. Secondly, in general terms the properties in the tentative lists are adjudged to be acceptable for nomination to the World Heritage List.
São Luis do Maranhão
Conjunto minero (Diamantina, Tiradentes, Mariana)
Chiloe group (churches only)
Santa Fe de Antiquoia
Villa de Leiva
San Cristobal Casas
San Luis Potosí
San Miguel Allende
Colonia de Sacramento
Nueva Cadiz (ruins)
Two points needs to be emphasized with regard to this table. First, it represents the initial approach to the study, the definitive recommendations of which are given in the main text above. Secondly, in general terms the properties in the tentative lists are adjudged to be acceptable for nomination to the World Heritage List.
|Par Jean-Charles Moretti, 1999
IRAA du CNRS, Lyon, France
I. L'histoire du théâtre antique
Les édifices à gradins de la Crète minoenne mis à part, l'architecture théâtrale semble apparaître en Grèce dans le courant du VIe. s. av. J.- C., à l'époque où sont institués le programme des grands concours religieux et les règles de leurs épreuves. Dans le même temps furent sans doute créés trois types monumentaux pour recevoir les trois types d'épreuves distinguées par les Grecs. Les épreuves hippiques prenaient place dans l'hippodrome, les épreuves gymniques dans le stade et les épreuves dites « musicales », car elles avaient partie liée avec les Muses, dans le théâtre. Les édifices de spectacle du VIe s. accueillaient les spectateurs sur des gradins de bois, montés sur des échafaudages. Ils sont connus par des textes et par des représentations sur des vases. Les plus anciens vestiges de théâtres retrouvés remontent au Ve s. et se répartissent dans la péninsule hellénique entre la Béotie et le Nord-Est du Péloponnèse en passant par l'Attique. Tous les théâtres de Grèce ont en commun certaines caractéristiques. Leurs koilons sont adossés à des éminences naturelles, taillées ou aménagées pour l'occasion et si nécessaire complétées par des remblais que peuvent contenir des murs de soutènement. Les gradins de pierre, quand ils existent, prennent la forme de simples degrés, avec une face antérieure et un lit supérieur plans. Dans plusieurs édifices, seul le premier rang est occupé par des trônes derrière lesquels un terrain déclive accueillait les spectateurs assis par terre ou sur des bancs de bois. La partie centrale du koilon est toujours composée de gradins rectilignes. Parfois, elle est complétée par deux ailes de gradins qui, vers leurs extrémités antérieures, divergent par rapport à l'axe du monument. Aucun koilon n'est divisé par des circulations horizontales. L'orchestra est de forme allongée, trapézoïdale ou rectangulaire. Elle est accessible latéralement par de larges parodos, qui jamais ne sont obturées par des portes. Nulle part n'a été retrouvé de mur d'un éventuel bâtiment de scène, mais les textes dramatiques conservés ne laissent pas douter qu'il en existait au moins en Attique, construits avec des matériaux périssables. Parmi les édifices qui remontent au Ve s. le mieux conservé est celui de Thorikos (Attique, Grèce), mais le plus important au regard de l'histoire architecturale et littéraire est celui du sanctuaire de Dionysos Éleuthéreus à Athènes.
Une série de gradins rectilignes, taillés dans le rocher, a été trouvée à Syracuse et datée du Ve s. par comparaison avec les dispositifs de Grèce, bien que l'on manque d'arguments pour justifier une datation si haute. À l'époque classique les différents types de spectacles montés dans les théâtres de Grèce étaient connus en Sicile et la Grande Grèce, mais il n'existait pas en Occident de grands concours de musique, de danse et de drame. En l'absence de vestiges d'édifices qui aient pu recevoir ces divers spectacles, on suppose que les représentations étaient données dans des constructions éphémères, comparables à celles représentées sur les vases dits « phlyaques », produits en Italie du sud entre le début et le troisième quart du IVe s. av. J.-C. Ceux-ci portent en effet la représentation de scènes de comédies attiques dans lesquelles les acteurs jouent sur des estrades de bois temporaires. Le recours à un tel équipement invite à croire qu'il n'était pas à cette époque d'édifice en pierre apte à recevoir les représentations.
Il s'en construisit plusieurs à partir de la seconde moitié du IVe s. et tout au long de l'époque hellénistique en Italie méridionale, à Locres et à Métaponte, mais plus encore en Sicile, à Akrai, Héracléa Minoa, Iaitas, Morgantina, Ségeste, Solonte, Syracuse ou Tyndaris, pour ne citer que les théâtres dont les vestiges sont les mieux conservés. Avec leurs koilons à gradins arqués et leurs bâtiments de scène à estrade haute, ils ne sont pas sans rappeler leurs contemporains de Grèce. Dans le détail, cependant, les différences ne sont pas négligeables. Les koilons sont en demi-cercle, mais rarement outrepassés. Le plus souvent les murs de soutènement antérieurs sont parallèles au front du bâtiment de scène. Les orchestras semi-circulaires ont des surfaces relativement réduites. Les parodos sont étroites, car les bâtiments de scène sont généralement proches deskoilons. Les proskènions sont de hauteurs comparables à ceux de Grèce, mais leurs fronts sont parfois murés et décorés d'atlantes ou de caryatides. Leur profondeur est dans plusieurs édifices relativement importante, atteignant 4,50 m et dépassant parfois les 6 m. Le front de l'étage desskènès donnant sur la couverture du proskènion est percé non pas de larges baies, mais de trois portes que les artistes atteignent par des escaliers situés à l'intérieur de la skènè. Dans plusieurs édifices, il est orné de colonnes doriques engagées et surmonté d'une sorte d'attique aveugle, lui aussi orné de pilastres ou de demi-colonnes. De part et d'autre du proskènion, la skènè présente dans plusieurs monuments des avant-corps à étages.
De telles différences morphologiques avec les théâtres de Grèce induisent un type d'utilisation des édifices scéniques en Italie du sud et en Sicile distinct de celui reconnu dans la péninsule hellénique et dans les Cyclades. En Occident, les acteurs jouaient habituellement sur le proskènion et non dans l'orchestra. Les modèles monumentaux mis au point en Grèce au début de l'époque hellénistique ont probablement eu une influence sur l'architecture théâtrale occidentale, mais ils n'ont pas été simplement exportés dans ces régions. Ils le furent en revanche en Orient ou, du moins, dans les grandes cités de la côte occidentale de l'Asie mineure, où furent construits, à partir de la fin du IVe s. av. J.-C., des édifices étroitement apparentés à ceux de Grèce.
Au début du Ier s. av. J.-C. apparaissent en Italie (Tusculum, Pompéi) des bâtiments de scène à estrade profonde (pulpitum) bordée par un front de scène percé de trois portes et orné de colonnes qui se dressent sur des podiums et sont détachées du mur de fond. Ces caractéristiques sont présentes dans le théâtre de type « romain » dont la gestation trouve son terme à Rome avec le théâtre de Pompée, en 55 av. J.-C., et celui de Marcellus, inauguré dans les années 20 av. J.-C. Le théâtre devient alors un édifice unitaire et indépendant du relief naturel. La conque semi-circulaire des gradins est portée par des murs rayonnants surmontés de voûtes, dont la maîtrise de l'opus caementicium facilite la réalisation. Dans cette structure creuse sont ménagés des passages couverts qui desservent les différentes zones de la cavea. Les gradins et parfois des tribunes réservées aux organisateurs des spectacles couvrent les parodos. La cavea est conjointe au bâtiment de scène, la longueur de celui-ci s'assimilant au diamètre de celle-là. Dans certains édifices un portique couronne les gradins. Peu développée, l'orchestra est pavée et reçoit les fauteuils mobiles des dignitaires. Tout le spectacle se déroule dorénavant sur la profonde estrade du bâtiment de scène. Un rideau, qui s'abaisse au début des spectacles, peut momentanément la cacher aux yeux des spectateurs. Derrière lui se dresse le front de scène, un mur dont le sommet règne avec celui de la cavea et qui, à ses extrémités, fait retour vers l'orchestra, définissant ainsi les flancs de l'estrade. Il est orné de placages de marbre, de statues contenues dans des niches et d'un ou de plusieurs niveaux superposés de colonnes dégagées. Derrière le mur de scène se trouvent généralement des vestiaires et des foyers. Les théâtres les mieux conservés du monde romain, ceux d'Orange (France), d'Aspendos (Turquie) et de Bosra (Syrie), portent la trace d'auvents qui couvraient le front de scène et l'estrade. Dans plusieurs monuments les gradins étaient ombragés par les vela, pièces de tissus montées sur des cordes, elles-mêmes fixées à des mâts.
D'une région à l'autre de l'Empire et à l'intérieur d'une même province, des théâtres de formes sensiblement différentes ont coexisté. La plupart des villes qui possédaient des édifices antérieurs au Ier s. av. J.-C. les ont conservés ou en ont seulement modifié le bâtiment de scène. En Asie mineure, où les traditions hellénistiques étaient fortement enracinées, le koilon adossé en demi-cercle outrepassé et le bâtiment de scène à estrade d'une hauteur équivalente à celle d'un proskènion restent fréquents. Le front de scène y est généralement percé de cinq portes alors qu'il n'en comporte que trois en Occident. Il est orné de colonnes implantées parallèlement à un mur de scène rectiligne, tandis que dans le reste de l'Empire des dispositions plus variées avec une ou plusieurs incurvations du mur et de la colonnade sont adoptées dès le Ier s. Dans les provinces d'Aquitaine, de Lyonnaise et de Belgique, le théâtre dit de type gallo-romain associe une cavea adossée, outrepassant souvent en demi-cercle et parfois garnie de gradins de bois, à un bâtiment de scène qui se réduit à une profonde estrade installée dans l'orchestra et à un mur de scène masquant la coulisse.
Apparu pour servir de cadre à des concours et plus généralement à des spectacles musicaux, orchestiques et dramatiques, le théâtre a aussi servi, au cours de son histoire, à d'autres réunions, dont certaines ont nécessité des transformations du bâtiment. Dans les cités de l'Orient grec il a reçu des assemblées politiques. Il a aussi servi, à l'époque impériale, pour des chasses et des combats de gladiateurs aussi bien en Gaule qu'en Orient ou en Afrique. Les gradins ont alors été séparés de l'orchestra par de fortes dénivellations, par des murets ou par des grilles et des filets, tandis que des refuges étaient aménagés pour les chasseurs. Quelques théâtres ont même été conçus dès leur construction pour les spectacles de l'arène. Certaines orchestras ont été transformées en bassins pour recevoir des mimes aquatiques, qui semblent avoir été prisés au IVe s.
II. L'histoire de l'amphithéâtre antique
L'amphithéâtre, comme son nom l'indique, se présente comme la combinaison de deux théâtres. Il comprend une arène autour de laquelle se développent des volées de gradins. Les édifices de Capoue et de Pouzzoles (Italie), construits à la fin du IIe s. av. J.-C., constituent les plus anciens exemplaires de ce monument, qui avait pour destination première d'accueillir des combats de gladiateurs. L'habitude d'organiser de tels spectacles n'était pas alors une nouveauté : dès le IIIe s. des combats sont attestés lors de funérailles en Étrurie et en Campanie. À Rome même, il s'en disputa pour la première fois en 264 av. J.-C., au forum Boarium, puis à maintes reprises sur le forum lui-même. La place, sous laquelle avaient été creusées des galeries de service, servait d'arène. Des gradins de bois érigés à l'entour recevaient les spectateurs. Apparu tardivement, l'amphithéâtre ne s'imposa pas comme le seul cadre des chasses et des combats de gladiateurs. Le premier amphithéâtre à Rome, construit en 29 av. J.-C., fut longtemps concurrencé par le Forum puis par le Champ de Mars.
À partir du Ier s. av. J.-C., cependant, les amphithéâtres se multiplient. L'arène revêt généralement un plan elliptique, qui est le plus favorable à la perception des spectacles par l'ensemble du public. Elle est accessible par des portes situées aux extrémités du grand axe de l'ellipse et complétées dans certains édifices par des accès sur son petit axe. Sous son sol sont aménagés à partir de l'époque augustéenne des chambres et des couloirs dont certains sont reliés à la surface par des trappes. Des monte- charges hissaient les bêtes destinées aux chasses. Une haute dénivellation couronnée d'un parapet sépare l'arène du public. Comme dans le théâtre, les gradins sont divisés horizontalement par des précinctiones définissant des maeniana et verticalement par des escaliers rayonnants limitant des cunei. Dans les édifices les plus anciens, l'arène était parfois creusée et la cavea était adossée au terrain naturel ou reposait sur du remblai qui, compartimenté ou non, était retenu par un mur à sa périphérie. Les accès aux gradins étaient alors disposés à l'extérieur du monument. Ce mode de construction resta majoritaire jusque dans les années 60 ap. J.-C., mais fut concurrencé à partir de la seconde moitié du Ier s. av. J.-C. par le dispositif à structure creuse adopté dans les théâtres. Des murs rayonnants reliés par des voûtes supportaient les gradins. Des galeries périphériques et des escaliers intégrés à la substructure de la caveaconduisaient à des vomitoires. La façade externe du monument se présentait comme une superposition de un à trois niveaux d'arcades et d'un attique décoré d'ordres engagés.
L'exemplaire le plus grand et le plus élaboré de ces édifices à substructions artificielles fut l'Amphithéâtre flavien de Rome, communément appelé Colisée. Commencé en 71 ou en 72 à l'initiative de Vespasien, il fut inauguré sous Titus par cent jours de spectacles durant lesquels cinq mille bêtes sauvages furent tuées. Le chantier fut achevé sous Domitien après plus de douze années de travaux. Son arène de 79,35 x 47,20 m était comprise dans une cavea de 187,75 x 155,60 m. Quelque cinquante-six rangées de gradins, divisées à l'image des groupes sociaux qui y siégeaient, pouvaient recevoir environ 60 000 personnes. Les premiers degrés recevaient les sièges mobiles des spectateurs de marque. Les derniers, construits en bois, étaient disposés sous un portique. La façade extérieure en travertin se composait de trois niveaux de quatre-vingts travées superposant les ordres dorico-toscan, ionique et corinthien. Un attique à pilastres corinthiens couronnait la construction. Percé de fenêtres et orné de boucliers, il portait les consoles utiles à la fixation des mâts du velum ombrageant les gradins. Un détachement de marins de la flotte était affecté au maniement des cordages de cette immense voilure. Dans son dernier état, le sous-sol de l'arène était entièrement aménagé et relié par un corridor souterrain à la grande caserne de gladiateurs située à proximité de l'amphithéâtre. L'édifice servit de modèle à de nombreux amphithéâtres construits dans l'Empire, sans néanmoins y imposer une uniformité planimétrique. En Gaule, il fut concurrencé par des monuments combinant une arène à une cavea incomplète.
En Occident, l'amphithéâtre fut de la fin du Ier s. au milieu du IIIe s. le signe le plus évident de la romanité et de l'urbanité. En Orient, en revanche, l'amphithéâtre connut une faible diffusion. Dans les pays où la culture grecque était bien implantée, peu d'amphithéâtres furent construits. Les théâtres et les stades furent souvent aménagés pour recevoir les spectacles de l'arène.
III. Critères proposés pour le classement des théâtres et des amphithéâtres
Les édifices devront répondre à plusieurs des sept critères ci-dessous énoncés. Les quatre premiers s'appliquent à la représentativité des monuments et les trois autres à leurs avantages documentaires :
|1||être un représentant insigne de l'un des différents types de théâtres ou d'amphithéâtres qui ont existé dans l'Antiquité|
- théâtre grec classique avec koilon à gradins rectilignes (type Thorikos), sans bâtiment de scène construit en pierre
- théâtre oriental hellénistique avec bâtiment de scène à proskènion et front de scène à baies et avec koilon à gradins en demi-cercles outrepassés (type Épidaure, Oropos ou Priène)
- théâtre occidental hellénistique avec bâtiment de scène à proskènion et front de scène à portes orné d'ordres engagés superposés et avec koilon semi- circulaire (type Ségeste ou Tyndaris)
- théâtre impérial de type micrasiatique avec front de scène à cinq portes et koilon en demi-cercle outrepassé (type Hiérapolis, Pergé ou Sidé)
- théâtre impérial avec front de scène à trois portes et cavea en demi-cercle soudé au bâtiment de scène. Dans cette catégorie, on distinguera les caveae adossées des caveae construites sur structures creuses et les différents fronts de scènes selon qu'ils sont rectilignes (type Philippopolis ou Aspendos), pourvus d'une niche médiane arquée et de deux niches latérales rectangulaires (type Orange ou Mérida), d'une niche médiane rectangulaire et de deux niches latérales arquées (type Bénévent ou Taormine) ou de trois niches arquées (type Lepcis Magna, Sabratha ou Bosra).
- théâtre gallo-romain (type Sanxay, Saint Marcel ou Drevant).
- théâtre avec front de scène et arène prévue dès la conception pour recevoir des chasses et des combats de gladiateurs (type Stobi ou Héraclée de Lyncestide).
Pour les amphithéâtres, on distinguera les édifices complets selon leur plan (oblong, circulaire ou elliptique) et selon leur structure (pleine ou creuse). Les édifices à arène (type Grand, France), où les gradins n'entourent pas l'aire sur toute sa périphérie, ne seront pas négligés.
2 avoir été un modèle architectural
L'évolution de la forme du théâtre et de l'amphithéâtre antique n'a pas été sans ruptures. Certains édifices ont marqué des étapes importantes dans la création des différents types et ont servi de modèles pour la réalisation d'autres monuments : ce fut le cas, à Rome, du théâtre de Pompée, de celui de Marcellus et du Colisée. D'autres édifices, sans avoir peut-être eu une grande importance dans l'histoire de l'évolution des types, demeurent pour nous les rares vestiges qui en illustrent la gestation : c'est le cas, par exemple, des théâtres de Thorikos (Grèce), de Tusculum, de Pompéi (Italie), d'Aphrodisias de Carie (Turquie) ou de l'amphithéâtre de Saintes (France), qui illustre la transition entre les structures pleines et les structures creuses.
3 avoir conservé les vestiges de nombreuses transformations
Certains théâtres ont été utilisés durant près d'un millénaire. Au cours de leur existence ils ont été transformés pour répondre à l'évolution des exigences des spectateurs et à celle des spectacles, recevant successivement les ressortissants de cités indépendantes puis les sujets d'un empire et des oeuvres musicales composées pour des concours puis des chasses ou des combats de gladiateurs donnés en l'honneur de l'empereur. Les vestiges de leurs différents états illustrent l'histoire des sociétés, des formes architecturales et des spectacles. Certains édifices, et en particulier plusieurs amphithéâtres, ont été largement transformés entre la fin de l'Antiquité et l'époque contemporaine. Ces transformations, trop souvent occultées par des restaurations modernes, devront être prises en compte pour évaluer la richesse de l'histoire architecturale des monuments.
4 avoir conservé des vestiges de son environnement antique
Les théâtres antiques se trouvaient généralement dans des villes ou dans des sanctuaires. Ils ont entretenu avec l'agora ou le forum, avec les temples des dieux du panthéon traditionnel ou avec ceux consacrés aux empereurs et avec les autres édifices de spectacle (odéons, stades, amphithéâtres) des relations fonctionnelles dont l'appréhension est nécessaire à la compréhension du rôle tenu par les monuments dans l'urbanisme, dans la religion et plus généralement dans la société antique. On favorisera donc le classement de complexes monumentaux comprenant des théâtres ou des amphithéâtres, plutôt que celui d'édifices isolés de leur contexte.
5 avoir conservé son authenticité
Les théâtres et les amphithéâtres n'ont pas seulement été restaurés au même titre que d'autres vestiges antiques. Depuis le XIXe s. l'habitude s'est prise de les réhabiliter pour recevoir des spectacles modernes. Ces réhabilitations ont souvent été très dommageables car les édifices antiques ne sont pas adaptés aux exigences des spectacles contemporains. Beaucoup ont déjà disparu sous les constructions de gradins et d'estrades modernes, de rambardes de sécurité et d'échafaudages destinés à porter l'éclairage ou la sonorisation. Certains édifices, pourtant bien conservés, ont ainsi été exclus du corpus des monuments pouvant être l'objet d'études scientifiques. Il serait souhaitable que le classement au patrimoine mondial non seulement n'accélère pas les réhabilitations abusives de monuments de spectacle, mais privilégie au contraire les édifices qui soit n'ont pas été restaurés, soit ont été l'objet de restaurations visant à expliciter leurs singularités antiques et non à les gommer par l'adjonction d'un équipement de salle de spectacle moderne.
6 avoir un bon état de conservation général
De nombreux édifices présentent des états de conservation très différents de leurs parties constitutives. Le théâtre d'Épidaure, par exemple, a un koilon remarquablement conservé et un bâtiment de scène dans un état médiocre, alors que celui d'Orange présente au contraire un mur de scène préservé sur 38 m de hauteur et des gradins presque totalement ruinés. On favorisera, autant que possible, le classement d'édifices dont toutes les parties constitutives ont un bon état de conservation : façade périphérique, gradins, circulations ainsi que, pour un théâtre, le bâtiment de scène et, pour un amphithéâtre, les salles de services sous l'arène.
7 être associé à des documents qui font connaître l'histoire de son utilisation
Les monuments ne sont pas seulement connus par leurs vestiges, mais par des documents archéologiques, littéraires ou épigraphiques, qui leur sont associés et qui permettent de préciser l'histoire de leur construction, de leur utilisation et de leurs transformations. On dispose pour certains édifices de comptes de constructions, de dédicaces, d'inscriptions mentionnant des réparations ou des aménagements, de textes, enfin, qui informent sur les spectacles dont ils ont été le cadre. C'est au Colisée que furent données les représentations commémorées par Martial dans le premier livre de ses Épigrammes et dans l'amphithéâtre de Lyon que fut martyrisée Blandine. C'est pour le théâtre du sanctuaire de Dionysos à Athènes, que furent écrites la plupart des pièces d'Eschyle, de Sophocle, d'Euripide et d'Aristophane qui sont conservées et qui sont devenues des oeuvres majeures de notre culture littéraire. Le souvenir de ces divers spectacles devra être pris en compte pour le classement.
|Jean-Charles MORETTI||Lyon, décembre 1999|
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