A bridge is a structure which is built over some physical obstacles such as a body of water, valley, or road, and its purpose is to provide crossing over that obstacle. It is built to be strong enough to safely support its own weight as well as the weight of anything that should pass over it. Bridges were and can be built out of different materials and in different designs, depending on its intended function, terrain where the bridge is built, the material used to make it, and the available funds.
The first bridges appeared in nature by themselves. A log could fall across a stream and form a natural bridge or stones could fall into a river from a nearby cliff. When humans started building bridges, they built them in simple form out of cut wooden logs or planks, stones, with a simple support and crossbeam arrangement, sometimes with use of natural fibers woven together to hold materials. One of the oldest arch bridges in existence is Arkadiko Bridge in the Peloponnese, Greece. It dates from 13th century BC.
Ancient Romans were the greatest bridge builders of ancient times. They built arch bridges and aqueducts some of which still stand today. They also used cement which consisted of water, lime, sand, and volcanic rock. Some of their most beautiful bridges were built over ravines while others were built over rivers where no rock or island emerges from the water to carry the piers.
Indians also built bridges, which is documented in their ancient text the Arthashastra which was written between 4th and 3rd century BC. They used plaited bamboo and iron chain as materials.
The Chinese oldest surviving stone bridge is the Zhaozhou Bridge. It was built from 595 to 605 AD during the Sui Dynasty. It is also it the world's oldest stone segmental arch bridge built with open spandrels.
Between 12th and 16th century many bridges were built with houses on them. They were solution for limited accommodation in walled cities and only France had as many as 35.
Inca civilization used rope bridges, a simple type of suspension bridge, in the 16th century. Hans Ulrich, Johannes Grubenmann, and others improved bridge-building in the 18th century. At the same time Hubert Gautier wrote a book on bridge engineering.
The Iron Bridge, built in Coalbrookdale, England in 1779, was one of the engineering marvels of the time because it used cast iron for the first time.
Industrial Revolution in the 19th century brings truss systems of wrought iron (an iron alloy with a very low carbon) but it did not have the tensile strength to carry the large weights. Enters steel, with its higher tensile strength, which replaces the iron and allows for much larger bridges. Gustave Eiffel, with his fresh ideas, was one of the first to use it.
The first welded road bridge in the world was built by welding pioneer Stefan Bryła in 1927.
With Industrial Revolution many different types of bridge appear and became possible because of technological advancements.