The bridge is in length with two towers, each high, built on piers. The central span of between the towers is split into two equal bascules or leaves, which can be raised to an angle of 83 to allow river traffic to pass. The bascules, weighing over 1,100 tons each, are counterbalanced to minimize the force required and allow raising in five minutes. The bascules are raised by huge hydraulic pumps which were first powered by steam engines. In 1976 these were replaced by oil and electricity. The bridge is made from more than 11,000 tons of steel, and covered with Cornish granite and Portland stone.