Cantilever bridge is a bridge whose main elements are cantilevers (structures that are anchored at only one end while the other projects horizontally into space). These bridges can use beams for smaller (pedestrian) bridges or trusses made of structural steel, or box girders of prestressed concrete for larger bridges that carry road or rail traffic.
First cantilever bridges appeared in 19th century when a need for longer bridges presented itself. To solve the problem of length, engineers of that time found out that many supports would distribute the loads among them and help to achieve length. Predecessors of cantilever bridges were bridges with hinge points that were placed mid-span. The one to be the first to invent and patent a cantilever bridge was Heinrich Gerber which did it in 1866. His first cantilever bridge was the Hassfurt Bridge over the Main River in Germany. It wasn't too impressive by today's standards - it had 38 meters in length but is considered the first modern cantilever bridge. Other early cantilever bridges were the High Bridge of Kentucky, designed by C. Shaler Smith in 1877, the Niagara Cantilever Bridge designed by Charles Conrad Schneider in 1883, and the Poughkeepsie Bridge designed by John Francis O'Rourke and Pomeroy P. Dickinson in 1889. The Forth Bridge, the bridge over the Firth of Forth in the east of Scotland, is one of the most famous early cantilever bridges and it is that with a reason. It is a railway bridge built in 1890 whose full length is 2,528.7 m while its longest span has length of 520 m. It remained the bridge with the longest span in the world until Quebec Bridge wasn't built in 1919 with its span of 549 m.
Today's longest cantilever bridges by their longest span are still:
A simple cantilever bridge has two cantilever arms extending from opposite sides of an obstacle that has to be spanned and they meet at the center. Cantilever bridges can be built without false-works below nor temporary supporting towers and cables above. It is one of their great advantages. They are also of very rigid construction so they can carry large loads without threat for construction.