In the olden days people probably found that a fallen log across a stream provided them with a useful footbridge. In jungle areas, they could make a simple footbridge out of ropes of vines twisted together. When people began to find that their log and vine bridges could not carry carts and wagons, or large number of people across wider spans, they began to improve their bridges to meet their needs.
The most primitive form is the beam or girder bridge consisting of a rigid beam resting at either end on piers. The span may be increased by the use of beams.
A development of this is truss bridge, being a wooden or metal framework designed, especially for greatest strength.
As per written records, the first bridge of wooden beams resting on stone piers was built in 2230 B.C. across the river Euphrates in Babylon. After this an arched bridge of stone was constructed across Anio River in Italy about 600 B.C. Gradually a lot of improvements were made in the art of building bridges. In 1779, the first metal bridge was built over Severn River in England. In 1887, the first reinforced concrete bridge was built over river Rhine in Germany.
Today due to the advancement in technology, engineers and architects are able to make very long and strong bridges. Usually bridges are divided into four categories: (1) Girder or beam bridges, (2) Arched bridges, (3) Suspension bridges and (4) Movable bridges. Nowadays the bridges are being built over very wide rivers. The construction of double-storeyed bridges too has become easy. One storey of such bridges is used for road transportation and the other for trains. The most common temporary bridges are pontoon or floating bridge comprising of floating members that support a continuous road way.
The longest bridge of the world is Humber Estuary Bridge of England. A sum of 67 million pounds was spent on its construction. The world’s widest long-span bridge is Sydney Harbour Bridge of Australia. It is 502.9 metres long and 48 metres wide. The highest bridge of the world built over Arkansas River of U.S.A. stands 321 metres (1053 ft) above the sea level.