For ages man has built bridges to allow transport over streams, rivers, gorges, and other transportation routes. The primitive clapper bridge--a stone slab-and-pier construction--and the basic beam bridge in which a stone or tree breached a gap, are among the earliest bridges.

The Romans used the semi-circular masonry arch in their bridge-building and also used timber, while in China segmental arch bridges were constructed to span greater distances. As commerce escalated, the load requirements of roads and bridges became greater, and complex bridge engineering was crucial to ensure against collapses. The late eighteenth century saw the introduction of iron and steel into bridge-building, with the stronger cast-iron eventually replacing wrought iron. The bridge-builders of Great Britain were particularly innovative and showed a keenness for competition. Such names as Thomas Telford and Isambard K. Brunel are associated with magnificent early suspension bridges.

Bridges are of three basic types that...