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A suspension bridge is any type of bridge that makes significant use of tension rather than or in addition to compression.[citation needed] A suspension bridge usually has main cables (else ropes or chains), anchored at each end of the bridge. Any load applied to the bridge is transformed into a tension in these main cables. The earliest suspension bridges had the cables anchored in the ground at either end of the bridge, but some modern suspension bridges anchor the cables to the ends of the bridge itself.
The earliest suspension bridges had no towers or piers, but these are present in the majority of larger suspension bridges. Although the earlier types of suspension bridges are suitable only for relatively short spans, all of the 14 longest bridges in the world are suspension bridges (see List of longest suspension bridge spans). Ignoring the possibility of pre-Columbian trans-oceanic contact, there were two independent inventions of the suspension bridge, in Eurasia (probably in China) and in Central and South America.
1. Simple suspension bridge: the earliest known type of suspension bridge, and usually a footbridge. The deck is flexible and lies on the main cables, which are anchored to the earth.
2. Underspanned suspension bridge: an early 19th century descendant of the simple suspension bridge. The deck is raised on posts above the main cables.
3. Stressed ribbon bridge: a modern descendant of the simple suspension bridge. The deck lies on the main cables, but is stiff, not flexible.
4. Suspension bridge: the most familiar type. Though technically all the types listed here are suspension bridges, when unqualified with adjectives the term commonly refers to a suspended-deck suspension bridge,. This type is suitable for use by heavy vehicles and light rail The main cables are anchored to the earth. The deck is carried below the main cables by "suspenders" and usually is stiff.
5. Self-anchored suspension bridge: a modern descendant of the suspension bridge, combining elements of a cable-stayed bridge. The main cables are anchored to the ends of the decks.
