The Tower Bridge was the answer to the problem. Two massive piers were sunk into the river bed to support the construction, and over 11,000 tonnes of steel provided the framework was clad in Cornish granite and Portland stone to protect the underlying steel work. Because of the fine masonry work of these towers, Tower Bridge is often mistaken for a stone bridge. It is a steel bridge however, and it depends entirely for its strength upon the steel columns and girders of which it is composed.
When it was built, it was the largest bascule comes from the French for ' see-saw'. The bridge could be raised to allow ships to sail through, and the mechanism to do this works on the principle of the see saw !