Because of this, Tower Bridge is sometimes confused with London Bridge, situated some 0.5 mi (0.80 km) upstream. Tower Bridge is one of five London bridges now owned and maintained by the Bridge House Estates, a charitable trust overseen by the City of London Corporation. It is the only one of the Trust's bridges not to connect the City of London directly to the Southwark bank, as its northern landfall is in Tower Hamlets.
A procession of vessels passed under the bridge. In 1878, City architect Horace Jones proposed a new bridge was needed to improve city traffic. It was approved by Act of Parliament in 1885 and the foundation stone was laid 21 Jun 1886. Including approaches, the bridge is a half-mile long, having a roadway 35-ft wide flanked by footways 12.5 ft wide.
From their foundations, the towers rise 293-ft, giving 140-ft clearance for ships beneath the central span which carries two footways. The roadway is a bascule (drawbridge), opening at the centre to permit ship traffic on the Thames. The piers also house the bascule-lifting machinery and their counterweights.
According to wikipedia