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BridgeThis article is about the edifice. For other meanings, see Bridge (disambiguation).
A bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle. The purpose of a bridge is to allow passage of people, vehicles, trains or ships over an obstacle. History The first bridges were spans made of wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. The arch was first used by the Roman Empire for bridges and aqueducts, some of which still stand today. The Romans also had cement, which reduced the variation of strength found in natural stone. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost. During the 18th century, many innovations in the design of timber bridges by Hans Ulrich and Johannes Grubenmann and others. With the rise of the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel. Etymology The Oxford English Dictionary traces the origin of the word bridge to an Old Norse word brygga, meaning "landing stage, gangway, or movable pier".. Types of bridge Bridges may be classified by their use or by the structure employed in their design. By use A bridge is usually designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. In some cases there may be restrictions in use. For example, it may be a bridge carrying a highway and forbidden for pedestrians and bicycles, or a pedestrian bridge, possibly also for bicycles An aqueduct is a bridge that carries water, resembling a viaduct. Decorative and ceremonial bridges To create a beautiful image, some bridges are built much taller than necessary. This type, found in oriental gardens, is called a Moon Bridge, evoking a rising full moon. Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, China. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants. Types of bridges Notable bridges See also External links
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