"Any building that allows passage over a ravine or river," says the dictionary. Old English brycge, from Proto-Germanic *brugjo (source also of Old Saxon bruggia, Old Norse bryggja, Old Frisian brigge, Dutch brug, Old High German brucca, German Brucke), from PIE root *bhru "log, beam," therefore "wooden causeway" (source also of Gaulish brug, Old High German brucca, German Brucke). The original meaning was "causeway made of logs" or "wagon bridge." In modern English usage, a bridge is "a structure that spans a gap in order to connect two parts of a surface" (or something like that - I'm not a native speaker). A road bridge connects two sets of traffic lanes; a footbridge connects two areas of an open space; a railroad bridge connects one section of track with another; etc. Many words are borrowed from other languages to describe various kinds of bridges. For example, "viaduct" comes from Latin via ferrata and French chemin de fer. The earliest known reference to the word "bridge" is in the 11th century, when it was used to describe a small wooden structure over a stream or river. Later on, during the Middle Ages, bridges became more and more important elements of large cities. They were usually built by local authorities or community groups and they served many purposes: military, economic, social... You name it! During wars, for example, towns would destroy their bridges so the enemy couldn't use them to attack them.