Why does Tower Bridge lift?
Historically, the River Thames has been an important trade route for Britain. The Pool of London which cuts through the city, was one of the busiest ports in the world when the Tower Bridge was built. Cargo shops from all over carrying important goods such as cotton, sugar, and tea came here. The goods would then be offloaded into warehouses along the river banks between London Bridge and Limehouse in East London.
As East London became more popular, there was a need for a newer crossing for the Thames. However, the bridge needed to not obstruct the large vessels carrying these goods. Therefore, a design that included bascules, or opening roadways, was selected for the bridge in the late 1800s.
Today, however, most boats on this part of the Thames are tourist boats.