Tower Bridge

10 min read

Tower Bridge is one of London's most successful architectural deceptions. Its turrets, battlements, pointed windows and pale stone make it look like a surviving fragment of medieval London, somehow extending the neighbouring Tower of London across the Thames. In reality it opened in 1894. Beneath the Gothic costume is an enormous Victorian steel machine, assembled with millions of rivets and designed to solve an extremely modern problem: how to carry London's rapidly growing road traffic across one of the busiest commercial waterways in the world without preventing ships from reaching the docks upstream.

Even its name encourages the wrong conclusion. Tower Bridge is not called Tower Bridge because it has two towers. The name refers to the Tower of London beside it; proposed designs existed before the familiar towers had even been decided upon. Its castle-like appearance came partly from the requirement that whatever enormous new structure appeared here should not overwhelm its far older neighbour.

The bridge exists because Victorian London had developed a serious geographical problem. By the second half of the nineteenth century the East End had expanded dramatically, with industry, docks and a population approaching a million people east of London Bridge. Yet London Bridge remained the lowest road crossing of the Thames. Getting from one side of the river to the other could mean a long diversion towards the City or reliance on ferries; journeys could take hours.

Building another ordinary bridge downstream sounded obvious until the importance of the river was considered. The stretch between London Bridge and what became Tower Bridge formed part of the Pool of London, surrounded by wharves and warehouses and crowded with vessels bringing goods from around the world. Thousands of substantial ships still needed to reach the Upper Pool each year. A fixed bridge low enough to be convenient for carts, horses and pedestrians would effectively have put a barrier across one of the commercial arteries of the British Empire.

London therefore needed two contradictory things in exactly the same place: an uninterrupted road and an uninterrupted shipping channel.

In 1876 the City of London established a Special Bridge or Subway Committee and invited ideas. More than fifty schemes were considered. Engineers proposed swing bridges, lifting bridges, rolling bridges, tunnels and extraordinary multi-level structures. Joseph Bazalgette — already famous for London's sewer system and Embankments — suggested high-level bridges that would simply pass above much of the shipping. Other proposals attempted to separate river and road traffic completely.

The process was hardly a model architectural competition. No winner emerged and the original competition was abandoned. One of the men involved in assessing the proposals was Horace Jones, the City Architect — who was simultaneously developing ideas of his own. The awkwardness is acknowledged even by Tower Bridge's official history. Eventually Jones joined forces with the civil engineer John Wolfe Barry and produced the scheme that was approved in 1884.

Their solution was not simply a lifting bridge. Tower Bridge is actually a combination of bridge types. The approaches on either side incorporate suspension structures, while the central roadway is divided into two enormous moving leaves called bascules. High above them, two walkways connect the towers and also form part of the structural system tying the bridge together. Historic England describes the result as a steel structure with Gothic towers, suspension side spans and a central opening bridge integrated into a single composition.

The word bascule comes from the French for a balance or seesaw, and that is essentially how the moving road works. Each half pivots around a shaft inside the river pier. The visible section projecting over the Thames is counterbalanced by an enormous weight moving through a hidden chamber behind the pivot. Each bascule weighs more than 1,200 tonnes, but a counterweight of roughly 400 tonnes means the machinery does not have to lift anything like that full mass from rest.

Some of Tower Bridge's most spectacular spaces are consequently ones most people never see. Inside each river pier is a vast bascule chamber around 27 metres high. When the bridge opens, the counterweights descend into these cavernous brick-lined spaces as the road rises above the Thames. The towers that appear to stand solidly on massive stone piers are therefore partly wrapped around enormous moving machinery and voids.

Construction began in April 1886. Creating foundations in the middle of a tidal working river while allowing shipping to continue was one of the project's most difficult tasks. Iron caissons were sunk into the riverbed and excavated to depths approaching eight metres below it, providing enclosed working areas from which the foundations for the two central piers could be constructed. The river could not simply be closed while the Victorians built their bridge around it.

The project rapidly became less the work of a single architect than a huge collaboration between engineering specialists. Wolfe Barry served as chief engineer, Edward Cruttwell as resident engineer and Henry Marc Brunel — the son of Isambard Kingdom Brunel — as assistant engineer. Horace Jones died in 1887, only about a year after construction began, and never saw the bridge that bears the visual stamp of his design.

What rose above the foundations was fundamentally a steel bridge. More than 11,000 tonnes of structural steel were fabricated for the towers and walkways, much of it by William Arrol & Co., the celebrated Scottish engineering company also involved with the Forth Bridge. An additional 1,200 tonnes of ornamental cast iron formed part of its contract. The steel skeleton was then enclosed in brick and clad with Cornish granite and Portland stone.

This is the key to understanding Tower Bridge's appearance. The masonry does not work like the load-bearing stone of the medieval Tower beside it. It protects and disguises an industrial frame. Look through some of the windows and internal spaces and the Victorian steelwork becomes visible behind the Gothic architecture. What seems at first to be a castle is closer to an extraordinarily elaborate stone casing around a piece of nineteenth-century infrastructure.

That disguise was deliberate. The competition demanded architecture appropriate to the setting of the Tower of London, and the final design uses pointed arches, pinnacles, turrets, steep roofs and fortress-like masonry to make an unprecedented piece of engineering look as though it belongs beside a medieval royal castle. There is even French château influence in the towers.

The effect can obscure just how technologically ambitious the bridge was. Its moving spans were originally operated not directly by steam engines but through a sophisticated hydraulic energy-storage system. Coal-fired boilers produced steam to power pumping engines. Those pumps forced water under pressure into six large accumulators, which stored energy until a ship required the bridge to open. High-pressure water could then be released to hydraulic drive engines, whose pistons turned huge cogs engaging with the bascules.

The accumulators were the Victorian equivalent of batteries. The boilers and pumps could steadily build up stored hydraulic pressure even while the bridge was closed, so enormous amounts of power were immediately available when an opening was required. It was an elegant answer to the problem of repeatedly moving roadways weighing more than a thousand tonnes while keeping waiting times manageable.

The high-level walkways were intended to solve the remaining inconvenience. A ship might interrupt horses and vehicles on the roadway, but pedestrians could climb the towers and continue across the river 42 metres above the Thames even while the bascules were open. The walkways were therefore not originally sightseeing platforms. They were part of the bridge's transport system.

Londoners largely rejected the walkways. Climbing all those stairs proved less attractive than simply waiting a few minutes for the bridge to close again. The walkways were used so little that they were closed to the public in 1910. One of the most visually distinctive components of Tower Bridge had failed in its intended everyday purpose only sixteen years after opening. They remained inaccessible to ordinary visitors until 1982, when they reopened as part of the Tower Bridge visitor attraction.

Before any of that could be discovered, London celebrated the completion of what had taken eight years to build. On 30 June 1894 the Prince of Wales, the future Edward VII, formally opened Tower Bridge accompanied by Princess Alexandra and their son, the future George V. When the bascules rose, the first vessel through was the harbour master's cutter Daisy, followed by a ceremonial procession of ships.

The demand for the new crossing became obvious almost immediately. When it opened to pedestrian traffic in July 1894, more than 140,000 people crossed on the first day. By later that month an estimated 60,000 pedestrians and 8,000 horse-drawn vehicles were using it daily. This was not a decorative civic monument looking for a function: Victorian London had been waiting for it.

The river remained just as important. In its first year the bridge opened 6,194 times — an extraordinary average of roughly seventeen lifts every day. Bridge staff effectively watched continuously for vessels requiring passage, clearing the road and raising the bascules as ships approached.

That figure also tells the story of the vanished London around it. Today's riverside apartments, offices, restaurants and tourist attractions occupy a landscape that was once one of the busiest working ports on earth. Tower Bridge was designed around a Thames packed with commercial shipping. As London's docks migrated downstream and containerisation helped destroy the old upriver port, the need for constant bridge openings collapsed. By the late 1960s there were only a few hundred lifts a year.

The bridge nevertheless remained a working machine, sometimes with dramatic consequences. On the evening of 30 December 1952, route 78 bus driver Albert Gunter was crossing Tower Bridge when the bascule beneath him unexpectedly began to rise. Faced with the prospect of the bus sliding backwards or becoming trapped, he accelerated. The double-decker cleared the widening gap and landed on the other half of the bridge. Everyone survived, and Gunter received a £10 reward for his quick thinking.

By then the machinery below was already becoming an anachronism. The original system required boilers to be fired and teams of workers to maintain steam pressure around the clock. From 1974 the machinery was modernised, and in 1976 the bridge became fully electro-hydraulic. Electric pumps now pressurise oil rather than steam engines pressurising water, but the basic mechanical principle remains beautifully Victorian: counterbalanced bascules rotating on their pivots while great cogs drive them open and closed. The original steam engines, pumps and accumulators survive in the Engine Rooms.

Even the colours most people associate with Tower Bridge are relatively recent. Its ironwork was originally painted a bright chocolate brown. Before the Second World War the bridge was given a more subdued grey camouflage scheme. The red, white and blue treatment familiar today dates from its repainting for Elizabeth II's Silver Jubilee in 1977.

The next transformation was cultural rather than mechanical. In 1982 the long-closed walkways reopened as part of an exhibition inside the bridge. Their original transport function had become unnecessary, but their position high above the Thames made them ideal viewing galleries. Glass floors added in 2014 now allow visitors to stand above the roadway and, during a lift, watch the bascules separate beneath their feet.

The bridge has consequently reversed one of its original relationships. In the 1890s the high-level walkways existed so pedestrians would not have to wait for ships. Today people deliberately wait for the ships because watching Tower Bridge open has become an attraction in itself.

Remarkably, river traffic still has priority under circumstances established by the bridge's original purpose. City Bridge Foundation states that registered vessels with a mast or superstructure of at least 30 feet can request an opening with 24 hours' notice, at no charge. The bridge can be required to lift at any time of day or night, throughout the year. A yacht on the Thames can therefore still stop road traffic across one of London's busiest landmarks because the fundamental bargain made with nineteenth-century shipping has never entirely disappeared.

Tower Bridge is unusual because its architecture encourages us to look at almost exactly the wrong things. The stone towers attract attention, but the important structure is the steel skeleton behind them. The picturesque upper walkways seem decorative, but they help tie the bridge together and were originally pedestrian bypasses. The enormous towers appear solid, while giant counterweights move through hidden chambers beneath them. The famous blue suspension elements are not merely ornament, and the apparently medieval bridge is younger than the Eiffel Tower.

It is also not quite the monument to Victorian certainty that its monumental appearance suggests. The design took years of argument. Its architect died before it was completed. Contemporary critics sometimes thought it ugly or dishonest. One of its major transport features was so unpopular that it closed. Its original steam machinery became obsolete, and the great commercial port it was designed around disappeared.

Yet almost everything essential worked. Tower Bridge successfully reconciled road traffic with shipping, wrapped advanced engineering in architecture capable of standing beside the Tower of London, and created a structure robust enough to continue performing its original mechanical trick more than 130 years later.

The most interesting way to look at it, then, is not as London's imitation medieval castle. It is a gigantic Victorian machine that became so familiar we stopped noticing the machine.