Tower Bridge, a double leaf bascule, opening

A bascule bridge is a drawbridge with a counterweight that continuously balances the span, or "leaf", throughout the entire upward swing in providing clearance for boat traffic. Bascule is a French term for seesaw and balance, and bascule bridges operate along the same principle. They are the most common type of movable bridge in existence because they open quickly and require relatively little energy to operate.

Although the bascule bridge has been in use since ancient times, it was not until the 1880s that engineers developed the ability to move very long, heavy spans quickly enough for practical application. Tower Bridge in London was the first large bascule bridge and is probably the most famous bascule bridge in the world.

Types of bascule bridges

• Scherzer rolling lift bascule bridge
• Rall bascule bridge - patented by Theodore Rall in 1901.
• Strauss bascule bridge - patented by Joseph Strauss.
• Chicago or fixed-trunnion bascule bridge