Although prehistoric in appearance, many examples date from the Middle Ages or later and have often been rebuilt. They’re mainly found in areas where suitable materials were easy to come by, such as the Pennines and Dartmoor (above).
The single arch transfers the weight of the bridge and whatever’s on it into a horizontal thrust, which is held by the abutments on the two banks. With a 90-foot arch, Twizel Bridge in Northumberland is the largest medieval single-span bridge in the country.
Because canals often cut across estates, farmlands and existing roads, large numbers of bridges were built to solve the problem. Many are hump-backed with a high single arch to allow barges and the horses that pulled them to pass underneath.
By using cables held up by towers to shift weight to an ‘anchorage’ at either end, suspension bridges can span large widths far more cheaply than a masonry bridge. Britain’s first road suspension bridge was built across the Tweed in 1819–20 (above).
These bridges have one or two counterweighted leaves that can pivot upward to allow boats to pass through. They vary in size, from London’s enormous Tower Bridge to small, hand-operated affairs on some of Britain’s canals.
Weight is transferred by the arches to the bridge’s supporting piers. Initially they were made of timber, but after the Norman Conquest stone was frequently used. Many are still in use, such as Clopton Bridge in Stratford-upon-Avon (above).