A bridge is a engineered structure built to span a gorge, road, river, or other body of water. Famous bridges include the Golden Gate Bridge in San Fransisco, the Brooklyn Bridge in City of New York, the Mackinac Bridge in Michigan, the Firth of Forth railway bridge in Scotland,...
The first bridges were simple wooden planks spanning a stream or such; the next examples found use stone, but again as a simple support and crossbeam arrangement. The arch was first used by the Roman Empire for bridges, and many Roman bridges still exist today. The Romans also had cement, which reduced the variation of strength found in natural stone. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost.
With the advent of the Industrial Revolution of the 19th century, Truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads. With the advent of steel, with its high tensle strength, much larger bridges were built; many using the ideas of Gustave Eiffel, which were first shown at the Eiffel Tower in Paris France.
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