Bridge is a combined bascule and suspension bridge over the River
Thames. It is close to the Tower of London, which gives it its name.
It has become an iconic symbol of London and is sometimes mistakenly
called London Bridge, though London Bridge is in fact the next bridge
upstream. In the second half of the 19th century, increased commercial
development in the East End of London led to a requirement for a
new river crossing downstream of London Bridge. A traditional fixed
bridge could not be built because it would cut off access to the
port facilities in the Pool of London, between London Bridge and
the Tower of London.
Jones' engineer, Sir John Wolfe Barry devised the idea of a bascule
bridge 800ft (244m) in length with two towers each 213ft (65m)
high, built on piers. The central span of 200ft (61m) between the
towers was split into two equal bascules or leaves, which could
be raised to an angle of 83 degrees to allow river traffic to pass.
The bascules, weighing over 1,000 tons each, were counterbalanced to
minimize the force required and allow raising in five minutes. The
two side-spans are suspension bridges, with the suspension rods anchored
both at the abutments and through rods contained within the bridge's
Construction started in 1886 and took eight years. With five major
contractors – Sir John Jackson (foundations), Baron Armstrong (hydraulics), William Webster, Sir H.H. Bartlett, and Sir William Arro
and employed 432 construction workers. Over 11,000 tons of steel provided
the framework for the towers and walkways. This was then clad in Cornish
granite and Portland stone, both to protect the underlying steelwork
and to give the bridge a pleasing appearance.
The Prince of Wales, the future King Edward VII, and his wife, Alexandra
of Denmark, opened the bridge on 30 June 1894. The original raising
mechanism was powered by pressurised water stored in six hydraulic
accumulators. In 1974, the original operating mechanism was largely
replaced by a new electro-hydraulic drive system. The only components
of the original system still in use are the final pinions, which engage
with the racks fitted to the bascules. Modern hydraulic motors and
gearing using oil rather than water as hydraulic fluid.
Some of the original hydraulic machinery has been retained, although
it is no longer in use. It is open to the public and forms the basis
for the bridge's museum, which resides in the old engine rooms on the
south side of the bridge. The museum includes the steam engines, two
of the accumulators and one of the hydraulic engines that moved the
bascules, along with other related artifacts. The high-level walkways
between the towers were closed in 1910; they have been reopened as
part of the Tower Bridge Experience, an exhibition mostly housed in
the bridge's twin towers. River traffic is now a fraction of what it
used to be, but it still takes priority over road traffic, 24 hours'
notice is required before opening the bridge.