Viaduct

A viaduct is a long bridge made of a series of arches, piers, or columns that carries an elevated road or railway across a valley, river, or other low ground at a roughly constant height, allowing the route to continue directly rather than following the terrain up and down. The word is a nineteenth-century coinage from the Latin via, meaning road, and ducere, meaning to lead, formed by analogy with the ancient Roman aqueduct, and early viaducts commonly used the same evenly spaced round arches the Romans had used for their own water-carrying structures. Viaducts let railways and roads cross valleys, urban areas, and rail yards without interrupting the traffic below; the tallest example, the Millau Viaduct in France, has a pier summit rising 343 meters, while China's Danyang-Kunshan Grand Bridge was the longest bridge in the world as of 2011. The arched space beneath many urban viaducts, especially in Britain, has since been converted into parking, retail, and workshop space.