bridge

A bridge is a structure designed to span an obstacle, such as a river or valley, allowing vehicles, pedestrians, and other loads to pass across. Most bridges consist of a flat deck, supported by beams, arches, or cables. These structures rest on a foundation that is carefully designed to transfer the weight of the bridge to the subsoil without settling.

Bridges can be constructed in a wide variety of forms, determined by the location, intended purpose, and available construction technologies. Simple bridge structures include beam bridges made from logs, and suspension bridges made of ropes or vines. The Romans and ancient Chinese built major arch bridges of timber, stone, and brick. During the Renaissance, advances in science and engineering led to wider bridge spans and more elegant designs. Concrete was perfected in the early nineteenth century, and arch bridges are now built primarily of concrete or steel.