A bridge is a structure designed to provide continuous passage over something. Bridges usually carry trains, cars, water, or power lines. There are about eight kinds of bridges, beam, cantilever, arch, truss, suspension, cable-stayed, movable, and floating bridges.
             Beam bridges are the most simple to build bridges. It is just a beam that is supported at both ends. These were the first bridges to be used. Beam bridges are the most commonly used in highway overpasses.
             Cantilever bridges are a more complex version of the beam bridge. On a cantilever there are two towers and the two bridges build out and meet in the middle. One example is the Quebec Bridge over the Saint Lawrence River.
             Arch bridges are characterized by their arches that support them. They are very stable. They have been constructed from wood, brick, stone, steel, and concrete. The Greek, Chinese, and Etruscans used these for transportation and to carry water.
             Truss bridges are strong and stable. Trusses are made by making the material into a triangle. These work well because the trusses that make it up all support some weight. Other bridges to can be built using trusses. One example of a truss bridge is the Astoria Bridge over the Colombia River.
             Suspension bridges consist of two large towers on each end of the bridge, these hold up the cables that are attached to smaller cables that hold the bridged it self. The end of the cables are buried in enormous concrete blocks called anchorages. Suspension bridges are used for the longest spans. They are expensive to. But the bridge is very flexible and can distort the road. These bridges are mainly used for transportation and not for trains, because trains are heave and travel fast.
             Cable stayed bridges are like the suspension bridge. There are two towers at the ends but the cables are connected directly to the towers and not to a main cable. This is good because it lacks the need
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