Bridges have come a long way since ancient times, when people used logs or weaved vines to cross streams. In fact, they have become an art form.
The most common types of modern bridges include: beam, truss, arch, cantilever, cable-stay and suspension. A beam bridge, the simplest type of bridge, is made of long beams of wood, metal or concrete that are supported at each end by piers. In a truss bridge, the beams are arranged in a lattice pattern. Many railroad bridges are truss bridges.
Arch bridges feature roads built on top of arch curves. Arch bridges are made of steel, concrete or masonry. The Natchez Trace Bridge in Franklin, Tennessee, is an arch bridge.
Suspension bridges are usually longer than other types of bridges. The road is suspended in the air on long cables that extend from one end of the bridge to the other. The cables sit atop tall towers and are secured on both sides by anchorages. The Golden Gate Bridge in San Francisco is a suspension bridge.
Cable-stayed bridges look a lot like suspension bridges, but the cables are attached directly to supporting towers and are secured to the roadway. The Leonard Zakim Bridge in Boston is an example of a cable-stayed bridge.