A bridge of concrete and steel that floats may seem highly unusual, if not impossible, but there are twenty such bridges around the world, five in the U.S. state of Washington alone, of which four are the longest floating bridges in the world.

Floating bridges, also known as pontoon bridges, are usually temporary structures built out of wood during times of emergencies such as war. Wooden floats and sometimes boats are lashed together and flat planks are laid over creating a roadway, allowing men and materials to cross bodies of water. Pontoon bridges have been used to great advantage in many battles throughout history, including the Second World War and during the Iran–Iraq War.

Homer Hadley Floating Bridge and Lacey V. Murrow Memorial Bridge. Photo credit: Atmoc Taco/Flickr