Tower Bridge is a combined bascule and suspension bridge in London, built between 1886 and 1894. The bridge crosses the River Thames close to the Tower of London and has become an iconic symbol of London. As a result, it is sometimes confused with London Bridge, about half a mile upstream. Tower Bridge is one of five London bridges 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.

The bridge consists of two bridge towers tied together at the upper level by two horizontal walkways, designed to withstand the horizontal tension forces imposed by the suspended sections of the bridge on the landward sides of the towers. The vertical components of the forces in the suspended sections and the vertical reactions of the two walkways are carried by the two robust towers. The bascule pivots and operating machinery are housed in the base of each tower.

The bridge deck is freely accessible to both vehicles and pedestrians, whereas the bridge's twin towers, high-level walkways and Victorian engine rooms form part of the Tower Bridge Exhibition, for which an admission charge is made. The nearest London Underground tube stations are Tower Hill on the Circle and District lines, London Bridge on the Jubilee and Northern lines and Bermondsey on the Jubilee line, and the nearest Docklands Light Railway station is Tower Gateway. The nearest National Rail stations are at Fenchurch Street and London Bridge.

Inception

In the second half of the 19th century, increased commercial development in the East End of London led to demands for a new river crossing downstream of London Bridge. A traditional fixed bridge at street level could not be built because it would cut off access by sailing ships to the port facilities in the Pool of London, between London Bridge and the Tower of London.

A Special Bridge or Subway Committee was formed in 1877, chaired by Sir Albert Joseph Altman, to find a solution. More than fifty designs were submitted, including one from civil engineer Sir Joseph Bazalgette, which was rejected because of a lack of sufficient headroom. A design was not approved until 1884, when it was decided to build a bascule bridge. Sir John Wolfe Barry was appointed engineer and Sir Horace Jones the architect (who was also one of the judges). An Act of Parliament was passed in 1885 authorising the bridge's construction. It specified the opening span must give a clear width of 200 feet (61 m) and a headroom of 135 feet (41 m). Construction had to be in a Gothic style.

Barry designed a bridge with two bridge towers built on piers. The central span was split into two equal bascules or leaves, which could be raised to allow river traffic to pass. The two side-spans were suspension bridges, with rods anchored both at the abutments and through rods contained in the bridge's upper walkways.

Construction

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 Arrol & Co. – and employed 432 construction workers. E W Crutwell was the resident engineer for the construction. The first stone was laid by Albert, Prince of Wales.

Two massive piers, containing over 70,000 long tons (78,400 short tons; 71,123 t) of concrete, were sunk into the riverbed to support the construction. More than 11,000 long tons (12,320 short tons; 11,177 t) of steel were used in the framework for the towers and walkways, which were then clad in Cornish granite and Portland stone, to protect the underlying steelwork.

Jones died in 1887 and George D. Stevenson took over the project. Stevenson replaced Jones's original brick façade with the more ornate Victorian Gothic style, which makes the bridge a distinctive landmark, and was intended to harmonise the bridge with the nearby Tower of London. The total cost of construction was £1,184,000 (equivalent to £136 million in 2019).

Opening

Tower Bridge was officially opened on 30 June 1894 by the Prince and Princess of Wales. An Act of parliament stipulated that a tug boat should be on station to assist vessels in danger when crossing the bridge, a requirement that remained in place until the 1960s.

The bridge connected Iron Gate, on the north bank of the river, with Horselydown Lane, on the south – now known as Tower Bridge Approach and Tower Bridge Road, respectively. Until the bridge was opened, the Tower Subway – 400 m to the west – was the shortest way to cross the river from Tower Hill to Tooley Street in Southwark. Opened in 1870, Tower Subway was among the world's earliest underground ("tube") railways, but it closed after just three months and was re-opened as a pedestrian foot tunnel. Once Tower Bridge was open, the majority of foot traffic transferred to using the bridge, there being no toll to pay to use it. Having lost most of its income, the tunnel was closed in 1898.

The high-level open air walkways between the towers gained a reputation as a haunt for prostitutes and pickpockets; as they were only accessible by stairs they were seldom used by regular pedestrians, and were closed in 1910. The walkway reopened in 1982 as part of the Tower Bridge Exhibition.

20th century

During the Second World War and as a precaution against the existing engines being damaged by enemy action, a third engine was installed in 1942: a 150 hp horizontal cross-compound engine, built by Vickers Armstrong Ltd. at their Elswick works in Newcastle upon Tyne. It was fitted with a flywheel having a 9-foot (2.7 m) diameter and weighing 9 tons, and was governed to a speed of 30 rpm. The engine became redundant when the rest of the system was modernised in 1974, and was donated to the Forncett Industrial Steam Museum by the Corporation of the City of London.

The southern section of the bridge, in the London Borough of Southwark, was Grade I listed on 6 December 1949. The remainder of the bridge, in the London Borough of Tower Hamlets, was listed on 27 September 1973. In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House, with the original final pinions driven by modern hydraulic motors.

In 1982, the Tower Bridge Exhibition opened, housed in the bridge's twin towers, the long-closed high-level walkways and the Victorian engine rooms. The latter still house the original steam engines and some of the original hydraulic machinery.

21st century

A computer system was installed in 2000 to control the raising and lowering of the bascules remotely. It proved unreliable, resulting in the bridge being stuck in the open or closed positions on several occasions during 2005 until its sensors were replaced.

In April 2008 it was announced that the bridge would undergo a "facelift" costing £4 million, and taking four years to complete. The work entailed stripping off the existing paint down to bare metal and repainting in blue and white. Before this, the bridge's colour scheme dated from 1977, when it was painted red, white and blue for Queen Elizabeth II's Silver Jubilee. Its colours were subsequently restored to blue and white. Each section was enshrouded in scaffolding and plastic sheeting to prevent the old paint falling into the Thames and causing pollution. Starting in mid-2008, contractors worked on a quarter of the bridge at a time to minimise disruption, but some road closures were inevitable. It is intended that the completed work will stand for 25 years.

The renovation of the walkway interior was completed in mid-2009. Within the walkways a versatile new lighting system has been installed, designed by Eleni Shiarlis, for when the walkways are in use for exhibitions or functions. The new system provides for both feature and atmospheric lighting, the latter using bespoke RGB LED luminaires, designed to be concealed within the bridge superstructure and fixed without the need for drilling (these requirements as a result of the bridge's Grade I status). The renovation of the four suspension chains was completed in March 2010 using a state-of-the-art coating system requiring up to six different layers of "paint".

On 8 July 2012, the west walkway was transformed into a 200-foot-long (61 m) Live Music Sculpture by the British composer Samuel Bordoli. 30 classical musicians were arranged along the length of the bridge 138 feet (42 m) above the Thames behind the Olympic rings. The sound travelled backwards and forwards along the walkway, echoing the structure of the bridge.

Following the Olympics, the rings were removed from Tower Bridge and replaced by the emblem of the Paralympic Games for the 2012 Summer Paralympics.

In 2016, Tower Bridge was closed to all road traffic from 1 October to 30 December. This was to allow structural maintenance work to take place on the timber decking, lifting mechanism and waterproofing the brick arches on the bridge's approaches. During this, the bridge was still open to water-borne traffic. It was open to pedestrians for all but three weekends, when a free ferry service was in operation.