The American bridge builder and engineer, David Steinman, speculates that nature did in fact provide the inspiration for the three major types of bridges—the corbelled arch, beam and suspension bridge, and that prehistoric man had found and used these. But one day a superman, who possessed extraordinary intelligence for his day, discovered that he was stranded without any of these bridges of nature to aid him at a time when he needed one badly. In a moment of brilliant thinking, he recalled the shape of such a structure—of, for example, the tree-trunk kind—and therefore he asked himself why he could not make or creates such a span. Necessity is the mother of invention, is it not? The human need for shelter bred architectural inventiveness. The human desire for entertainment led to music, art, dancing, and eventually card and video games, bingo sites, film and comedy. The urge to travel gave us the wheel, the car, the boat and airplane, roads and bridges.
We know that certain natural bridges were formed, that sustained themselves by the geometric principles of the arch. Such bridges, as those formed in Virginia and Arizona , attest to the strength of the arch. We also may reasonably surmise that the first bridges were such simple structures. There remains evidence of the “clapper” (from the Latin, claperius, meaning pile of stones) bridges in England, primitive rocks arranged for passage over rivers. These first beam, or stringer, bridges, were formed simply by laying a flat stone or log on supports without need for complex mathematical calculations or resolution of engineering problems.
By the same token, ropes and vines were used for carrying people over ravines and canyons. Perhaps someone first swung from one point to another, and later kept the vine or rope attached to two points so that cargo or persons could slide along from one end to the other. Eventually, these supports would hold another vine or rope over which people would walk, ultimately becoming a “roadway” in itself. Such may have been the origins of the suspension bridge.
The Romans, while certainly not the originators of the arch (credit has been given to the Babylonians for that), can fairly be said to have perfected its application and principles. Some of the stone arch bridges built by Roman engineers survive to this day.
These remarks are taken from my book, The Bridges of New Jersey, which is available in bookstores and from amazon.com and barnesandnoble.com.
For more background information on the types of bridges illustrated here, click on the below links
Arch Bridges Cable-Stayed Cantilever Covered Movable Suspension Truss Bridge Gallery Home Gallery Guide Background to Bridges