Pontoon bridge

Pontoon bridges are floating bridges supported by floating pontoons with sufficient buoyancy to support the bridge and dynamic loads. While pontoon bridges are usually temporary structures, some are used for long periods of time[1]. There are three permanent pontoon bridges that span Lake Washington in Washington state. One of these bridges, the Evergreen Point Floating Bridge (1963), is the longest floating bridge in the world, at 7,578 feet. It carries Washington State Route 520 across the lake from Seattle to Medina. The other two, the Lacey V. Murrow Memorial Bridge (6,620 feet) and the Third Lake Washington Bridge (5,811 feet), carry Interstate 90 across the lake from Seattle to Mercer Island. The world's longest floating bridge over salt water is also in Washington state, carrying Washington State Route 104 6,521 feet across Hood Canal. These four bridges are the four longest of their type in the world.

Pontoon bridges are especially useful in war to cross rivers. Such bridges are usually temporary, and are sometimes destroyed after crossing (to keep the enemy from using them), or collapsed and carried (if on a long march). They were used to great advantage in many battles throughout time, including the Battle of the Garigliano, the Battle of Oudenarde, and many other battles.