Originally, London Bridge was the only crossing over the Thames. As London grew, many bridges were added, but these were all to the west of London Bridge, since the area east of London Bridge had become a busy port. In the 19th century, the east end of London became so densely populated that public pressure mounted for a bridge to the east of London Bridge, as journeys for pedestrians and vehicles were being delayed literally by hours.
Finally in 1876, the Corporation of London, who were responsible for that part of the Thames, decided that the problem could be put off no longer.
The big problem for the Corporation of London was how to build a bridge downstream from London Bridge without disrupting river traffic activities. To get as many ideas as possible, the "Special Bridge or Subway Committee" was formed in 1876, and opened the design of the new crossing to public competition.
Over 50 designs were put forward for consideration but it wasn't until October 1884 that Horace Jones, the City Architect, in collaboration with John Wolfe Barry, offered the chosen design for Tower Bridge as a solution.
It took 8 years, 5 major contractors and the relentless labour of 432 construction workers to build Tower Bridge.
Two massive piers had to be sunk into the river bed to support the construction, over 11,000 tons of steel provided the framework for the towers and walkways.
When it was built, Tower Bridge was the largest and most sophisticated bascule bridge ever built ("bascule" comes from the French for "see-saw"). It was a hydraulically operated bridge, using steam to power the enormous pumping engines. The energy created was then stored in six massive accumulators so that, as soon as power was required to lift the bridge, it was readily available. The accumulators fed the driving engines, which drove the bascules up and down. Despite the complexity of the system, the bascules only took about a minute to raise to their maximum 86 degrees.
Nowadays, the bascules are still operated by hydraulic power, but since 1976 they have been driven by oil and electricity rather than steam. The original pumping engines, accumulators and boilers are on show as part of The Tower Bridge Exhibition.