A bridge is a structure that provides passage over obstacles such as valleys, rough terrain or bodies of water by spanning those obstacles with natural or manmade materials. They were first used in ancient times when first modern civilizations started rising in the Mesopotamia.
From then, knowledge, engineering, and manufacture of new bridge building materials spread beyond their borders, enabling slow but steady adoption of bridges all across the world.
In the beginning bridges were very simple structures that were built from easily accessible natural resources- wooden logs, stone and dirt. Because of that, they had ability only to span very close distances, and their structural integrity was not high because mortar was not yet invented and rain slowly but constantly dissolved dirt fillings of the bridge. Revolution in the bridge construction came in Ancient Rome whose engineers found that ground volcanic rocks can serve as an excellent material for making mortar. This invention enabled them to build much sturdier, powerful and larger structures than any civilization before them.
Seeing the power of roads and connections to distant lands, Roman architects soon spread across the Europe, Africa and Asia, building bridges and roads of very high quality.
After the fall of the Roman empire, bridge building techniques in Europe and Asia stagnated until the 18th century when a new age of science and engineering swept across the world. Architects of that time started using a new construction material – cast iron. Iron enabled creation of new bridge designs such as truss systems. Sadly, wrought iron did not have tensile strength to support heavy structures, which was later made possible with the adoption of steel and the designs of famous French architect and engineer Gustave Eiffel, builder of the Eiffel tower in Paris.
Modern bridges are usually made with a combination of concrete, iron and cables, and can be built from very small to astonishing lengths that span entire mountains, rough landscapes, lakes and seas.