Plans for the Tower Bridge were devised around 1876 when the east of London became extremely crowded and a bridge across the Thames in that area of the city seemed a necessity. It would take another eight years - and lots of discussions about the design - before construction of the bridge started.
The bridge, designed by city architect Horace Jones in collaboration with John Wolfe Barry, would eventually be completed in 1894. Five contractors and nearly 450 workers were involved in the construction of the 265 meter long bridge. It took 11,000 tons of steel to build the framework. At the time many people disliked its Victorian Gothic design, but over time the bridge became one of London's most famous symbols.
The proximity of the harbor and its location in the direction of the sea required for the bridge to allow the passage of large vessels. Hence the decision to create a moveable bridge which can be opened to accommodate boat traffic. The mechanism to open the bridge is hidden in the two towers. Until 1976, when the mechanism became electrified, steam power was used to pump water into hydraulic accumulators which powered the engines.
Each deck is more than 30 meters wide and can be opened to an angle of 83 degrees. When opened the bridge has a clearance of almost 45 meters. It used to open almost fifty times a day but nowadays it is only raised about one thousand times a year.
Bridge lifts are pre-scheduled (for cruise ships, etc) so visitors can check the bridge's website to find out when it will rise and lower.