Primitive people realized that when trees fell from one bank of a river across to the other, it made the river easy to cross. This was an early beam bridge. The simplest and least expensive bridge to construct, a beam bridge is a horizontal beam resting on piers. Beam bridges are only practical over short distances, where the span is not extensive. Longer distances present more challenges because of the limiting factor of the maximum practicable distance that can be supported by piers.
The suspension bridge was born in places like the forests of Peru and the foothills of the Himalayas, evolving from crude rope swings made from vines and creepers. The suspension bridge suspends, or hangs, the deck or roadway on cables. The intricate engineering involved makes the suspension bridge an expensive bridge solution, but its span can be considerably more than a beam bridge. The Golden Gate Bridge once held the record for the longest span, but now it is Japan's Akashi Kaikyo Bridge, with a main span of over 1.237 miles.
The arch is one of humanity's greatest ever discoveries, according to ICE. The arch, whose strength lies in its ability to carry loads along its curves to the supports, allowed the building of some of the greatest bridges and other structures in the world. In a case of necessity being the mother of invention, David Bennett ascribes the inventors as being the Sumerians, who discovered the arch through trial and error while building with adobe, or mud bricks, because of a lack of stone.
A truss bridge has a deck supported by a truss. A truss is a structure built of struts and bracing, often featuring triangular units. Although many previous bridges incorporated truss elements, the first true truss bridge was patented in 1820 by bridge builder Ithiel Town. He called it the Town Lattice. North American bridge builders erected many truss bridges in the 19th century as the railway network expanded. The first cantilever truss bridge was the Forth Rail Bridge, built in 1890.