Bridges
A bridge is a structure that crosses a river, lake, railroad, road, ravine, or other obstacle. Bridges perform a wide variety of functions, and can carry cars, trains, pedestrians, pipelines, utility lines, buildings, wildlife, and canals. Styles of bridges include arch, truss, beam, cantilever, suspension, and cable-stayed. Less common types of bridges are moveable bridges, double deck bridges, pontoon bridges, and military bridges. Bridges can also be categorized by their materials, which include wood, brick, stone, iron, steel, and concrete.