A viaduct is a bridge composed of several small spans. The term viaduct is derived from the Latin via for road and ducere to lead something. However, the ancient Romans did not use that term per se; it is a modern derivation from an analogy with aqueduct. Like the Roman aqueducts, many early viaducts comprised a series of arches of roughly equal length. Viaducts may span land or water or both.

The longest viaduct in antiquity may have been the Pont Serme which crossed wide marshes in southern France. Viaducts are commonly used in many cities that are railroad centers, such as Chicago, Atlanta, Birmingham, London, and Manchester. These viaducts cross the large railroad yards that are needed for freight trains there, and also cross the multi-track railroad lines that are needed for heavy railroad traffic. These viaducts keep highway and city street traffic from having to be continually interrupted by the train traffic. Likewise, some viaducts carry railroads over large valleys, or they carry railroads over cities with many cross-streets and avenues.

Many viaducts over land connect points of similar height in a landscape, usually by bridging a river valley or other eroded opening in an otherwise flat area. Often such valleys had roads descending either side (with a small bridge over the river, where necessary) that become inadequate for the traffic load, necessitating a viaduct for "through" traffic. Such bridges also lend themselves for use by rail traffic, which requires straighter and flatter routes. Some viaducts have more than one deck, such that one deck has vehicular traffic and another deck having rail traffic. One example of this is the Prince Edward Viaduct in Toronto, Canada, that carries motor traffic on the top deck as Bloor Street, and metro as the Bloor-Danforth subway line on the lower deck, over the steep Don River valley. Others were built to span settled areas and crossed over roads beneath - the reason for many viaducts in London.

Viaducts over water are often combined with other types of bridges or tunnels to cross navigable waters. The viaduct sections, while less expensive to design and build than tunnels or bridges with larger spans, typically lack sufficient horizontal and vertical clearance for large ships. See the Chesapeake Bay Bridge-Tunnel.

The Millau Viaduct is a cable-stayed road-bridge that spans the valley of the River Tarn near Millau in southern France. Designed by the French bridge engineer Michel Virlogeux, in collaboration with architect Norman Robert Foster, it is the tallest vehicular bridge in the world, with one pier's summit at 343 metres (1,125 ft)—slightly taller than the Eiffel Tower and only 38 m (125 ft) shorter than the Empire State Building. It was formally dedicated on 14 December 2004 and opened to traffic two days later. The viaduct Danyang–Kunshan Grand Bridge in China is the longest bridge in the world according to Guinness World Records as of 2011.

In Romance languages, the word viaduct refers to a bridge which spans only land. A bridge spanning water is called ponte.

Read more about Viaduct:  Past and Future, Gallery

Other articles related to "viaduct":

Stanford Viaduct
... Stanford Viaduct is a railway viaduct in Leicestershire and Nottinghamshire ... Presently, the viaduct is in use for gypsum trains, and diesel or steam heritage trains from the Nottingham Heritage Centre run on certain Saturdays and ...
London Road Viaduct - Architecture
... The piers are thicker on the outside than on the inside because the viaduct is constructed on a sharp curve trains reach the viaduct almost immediately after leaving the Brighton Main Line, and the. 10 million bricks were needed to build the viaduct ... Running along the top of the viaduct on both sides is a balustrade with stone balusters ...
London Road Viaduct - The Viaduct Today
... London Road Viaduct was listed at Grade II* by English Heritage on 19 April 1974 ... passenger trains (87 eastbound and 87 westbound), all operated by Southern, cross the viaduct each weekday ...
Solway Junction Railway - History
... The viaduct was designed by Sir James Brunlees, took 3½ years to build and cost about £100,000 ... In 1875 and 1881 the viaduct was damaged by ice, and by altering sediment-carrying currents it caused nearby Port Carlisle to silt up and lose trade ... On 1 September 1921 the viaduct was closed entirely ...
Viaduct - Gallery
... Viaduct of Tren a las Nubes in Salta, Argentina Renmin Lu Viaduct of the city of Guangzhou (formerly Canton) is the first viaduct built in mainland China The Patapat Viaduct in ... Built in 1903 The Cypress Street Viaduct was an example of a double decker freeway in Oakland, California which collapsed in the 1989 Loma Prieta Earthquake and was later demolished The Alaskan ... To be demolished in 2012 The Millau Viaduct, and the town of Millau, France on the right ...