A viaduct is a bridge composed of several small spans for crossing a valley , dry or wetland , or forming a flyover.
The term is conventional for a rail flyover as opposed to a flyingjunction or a rail bridge which crosses one feature. In Romance languages, the word viaduct refers to a bridge which spans only land . A bridge spanning water is called ponte.
The term viaduct is derived from the Latin via for road and ducere, to lead . The ancient Romans did not use the term; it is a nineteenth-century derivation from an analogy with aqueduct.
Like the Roman aqueducts, many early viaducts comprised a series of arches of roughly equal length .