Structure by means of which a path, road, etc., is carried over a ravine, valley, or other depression, or over a river or other water-course, affording passage between two points at a height above the ground level, and allowing a free passage through its one or more open intervals beneath the road, etc. Bridges vary in complexity of structure from a simple plank, log, or slab of stone supported at each end (or a single arch spanning from bank to bank, say), to a far more elaborate structure with architectural pretensions, featuring piers, arches, girders, chains, tubes, and many other elements. Early bridges were made of ropes, while timber bridges of various types have a long ancestry. Arched bridges of brick or stone go back to Antiquity, and some spectacular Roman bridges survive, such as the Pons Fabricius (62 bc), Pons Milvius (109 bc), and the Pons Aelius (now Ponte Sant'Angelo, completed ad 134), in Rome, but the Puente del Diablo near Martorell in Spain is even earlier (c.219 bc), although much restored, and seems to be one of the oldest still in existence. Also in Spain is the celebrated bridge over the Tagus at Alcántara (ad 105), with its six impressive arches. Many fine bridges were erected in medieval times (e.g. the fortified Pont Valentré over the Lot at Cahors, France (1308–80), and London Bridge over the Thames, on which habitable buildings stood: it was erected 1176–1209 to designs by Peter, chaplain of Cole Church, while elegant Classical structures (essentially based on Roman precedents) were built in C17 and C18 (e.g. Telford's Tay Bridge, Dunkeld, Perthshire (1806–9). Cast iron was first used for bridge-construction in C18 at Ironbridge, Salop. (1777–9). The development of canals and railways led to considerable advances in bridge-design, notably the suspension-bridge over the Menai Straits in Wales (1819–26) by Telford, the tubular girder-bridge also over the Menai Straits (1844–50) by Stephenson, and the Clifton suspension-bridge, Bristol (1831–64), by the younger Brunel. Other important designers of C19 bridges were Eiffel and Roebling. In C20 reinforced concrete was used to great effect by many designers, including Freyssinet, Hennebique, Maillart, and other elegant structures were erected by Ammann, Arup, Bonatz, and Calatrava, among others. The main types of bridge are:aqueduct:for conveying water (such as a canal). Good examples are the Roman Pont du Gard, near Nîmes, France (C1 bc) and Telford's Ponty-Cysyllte aqueduct (1795–1805);arch-bridge:carried on arches or vaults;bascule:a type of cantilever that can be raised in order to allow ships to pass under, e.g. London's Tower Bridge;cantilever:arm projecting from a pier, or with two arms projecting from piers and connected in the centre;clapper:stone bridge of piers with slabs of stone spanning between them;draw:one that can be drawn up or let down, hinged like a flap;girder:consisting of straight beam-like elements carried on piers, columns, or other supports;Palladian:bridge with colonnaded superstructure (e.g. at Wilton, Wilts. (1735–7);suspension:hung from chains or cables suspended from elevated piers;swing:swivelling bridge which revolves horizontally on a pivot;tubular:essentially a very large hollow-girder, carried on piers, through which traffic passes (e.g. Stephenson's Menai Straits railway-bridge (1844–50);viaduct:long structure carrying a road or a railway over a valley.
Subjects: Architecture — History.