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Before Tower Bridge was built, a ferry ran from Horselydown Steps, near
the southern foot of today’s bridge, to a point on the north bank known
as Dead Man’s Hole – so called because the ferrymen operated a lucrative
sideline taking corpses across the river. The reason was simple. Bart’s
Hospital, on the north side, paid 6d more for the bodies used for medical
research than Guy’s Hospital on the south.

Nearly a hundred years ago, this section of the river was finally spanned
when Tower Bridge opened on 30 June 1894. Until the Queen Elizabeth II Bridge
opened at Dartford in 1991, Tower Bridge was the only overpass downstream
from London Bridge. Its Victorian Gothic design has become famous, symbolising
London in much the same way as the Eiffel Tower evokes Paris and the Statue
of Liberty New York.

The bridge caused controversy that lasted from the time the first designs
were examined in the 1800s until it was finally built at the end of the
century. Supporting the bridge were land-based businesses, such as the
cart drivers in east London, that wanted a bridge to improve overland transport.
By the 1880s more than a million people lived east of London Bridge – a
third of the city’s population. West of London Bridge a series of new road
and railway bridges were built to serve the expanding city. But horse-drawn
traffic wanting to cross the river in east London was forced to cross the
Thames at London Bridge. A more easterly crossing would save at least an
hour on the journey.

Opposing its construction were powerful shipping interests that feared
a bridge would staunch the flow of river traffic. The stretch of water immediately
downriver from London Bridge, known as the Pool of London, was the commercial
hub of the British Empire. As the busiest waterway in the world, it carried
colliers from the north, clippers from the Indies and freighters from far-flung
colonies. Shipping companies and owners of wharves believed a new bridge
would prevent large ships passing, thereby strangling business for wharves
and docks upstream. Although Parliament strongly favoured an eastern crossing,
shipping was so important that the industry could effectively veto a bridge.
The result was political deadlock.

A charitable trust, the Bridge House Estates, was charged with resolving
the problem. Run by the City of London, the trust was set up in the 12th
century by King John to build the medieval London Bridge. It rebuilt London
Bridge in the 1820s and again in the 1970s. It also owns and maintains –
free of charge – Blackfriars Bridge, Southwark Bridge and Tower Bridge.

Tower Bridge is arguably its greatest achievement. More than fifty
designs were considered by the Bridge House Estates’ commissioners. To mollify
shipping interests, Parliament stipulated that designs should maintain
a navigable channel nearly 50 metres wide and 40 metres high.

In 1878 Horace Jones, the architect responsible for designing the City’s
public buildings, unveiled the concept of Tower Bridge. Influenced by bridges
over canals in the Netherlands, Jones produced a design for a brick bridge
with two towers. Spanning the river, between the towers, was a roadway that
could be raised by hydraulic power. The bridge was partly a suspension bridge
and partly a bascule bridge – bascule comes from the French word for seesaw.
The two halves of the roadway – the two bascules – were counterbalanced
by weights making them easier to lift. Most importantly, the design matched
the requirements laid down by Parliament.

But the civil engineer John Wolfe Barry realised that a brick structure
could not cope with the stresses of a roadway being raised and lowered and
he substantially reworked the design. The new design was for a steel bridge.
The Portland stone and granite of the central towers we see today have
no structural function. The stone is simply cladding to help the bridge
blend with its ancient neighbour, the Tower of London.

Tower Bridge took eight years to build – twice as long as expected,
chiefly because of the underwater work involved in laying the foundations.
From the surface, tall, wrought-iron chambers were sunk into the riverbed
and divers inside them shovelled mud from the bottom. As the mud was removed,
the chambers were sunk deeper until they became watertight and the water
could be pumped out. It cost £1.2 million (around £50 million
today). Ten workers were killed while it was being built – fewer than usual
for a project of this complexity.

The bridge was the most complicated steel structure of its time and
the mid-stream building site created difficult conditions for site engineers.
The lifting gear, for example, could not raise more than five tonnes of
steel from batches brought by barge from Scotland and the steel sections
had to be riveted together on site. Before Tower Bridge was built, riveting
was carried out manually. But a new hydraulic riveter, developed by site
engineer James Tuit, was used extensively to speed construction.

Weighed down by use

Just how well-engineered the bridge was can be seen by examining the
central bearings which carry the weight of the bascules. Bridge Master
Chris Stevens says the bearings were opened up about thirty years ago to
check for deterioration. The engineers took the covers off and put them
back on – the bearings were in perfect condition.

But the bearings are threatened by the sheer weight of modern traffic.
Lorries of more than 17 tonnes are banned from the bridge, but Stevens says
some lorry drivers ignore the ban and it is now necessary to adjust the
bearings more frequently.

Hydraulic power was a popular source of energy in Victorian times and
was duly employed to raise the roadway, allowing ships to pass. Victorian
steam engines could not provide enough energy to open the bridge quickly
so energy from steam power was stored hydraulically in a way that could
be released rapidly and efficiently. Vast steam engines on the south bank
of the Thames pumped water into high-pressure chambers containing enormous
weights. The rising water level lifted the weights and one-way valves prevented
the water from escaping when the engines stopped. When the energy was needed,
another valve at the bottom of the chamber was opened and the huge weights
forced water into the hydraulic system under enormous pressure. The high-pressure
water turned gears and cogs, opening the bridge in just one minute.

Tower Bridge was one of the earliest engineering structures to use the
modern principle of redundancy: the duplication of vital machinery needed
to open the bridge. Two boilers provided steam for two pumping engines,
and two pipelines lead to four pairs of lifting mechanisms. Just one boiler
and one pumping engine could provide the power to lift the bridge but two
allowed for breakdowns and servicing. And as if that wasn’t enough, the
bridge could also tap into a high-pressure ring main run by the London Hydraulic
Power Company. In Victorian London, hydraulic equipment, such as lifts
in hotels, was powered by high-pressure water from a main running under
the city.

Hydraulic power also operated the lifts to the high-level walkways for
pedestrian crossing when the main bridge was raised. But the walkways became
a noted trading place for prostitutes and were closed before the First World
War.

In its heyday, the bridge was opened 6000 times a year. It took 100
people to crew the bridge, move the coal, stoke the engines and maintain
the opening gear. But the decline of the docks after the Second World War
has meant that the bridge is not used as it once was.

In 1972 the City decided to modernise the lifting mechanism. Diesel
replaced steam as the source of power for the engines, oil replaced water
in the hydraulics and computers automated control of the traffic signals
and the raising of the bridge. Modern diesel engines provide enough power
to raise the bridge so the Victorian energy storage hydraulics are no longer
used. Stevens says that the bridge can still be raised on any day of the
year, but no longer opens on demand – crews now have to give 24 hours’ notice.

Although the commercial importance of Tower Bridge has declined, it
is rapidly becoming a tourist attraction. In 1982, the City of London decided
to open an exhibition at the bridge which proved more popular than anyone
expected. The exhibition includes a tour around the boiler house on the
south bank, which still has much of the original machinery.

But Tower Bridge is not just for the visitors and tourists. It opens
500 times a year, although these days naval boats, cruise liners and pleasure
craft have replaced the cargo ships. While I sat in the bridge master’s
office, Stevens took a telephone call from one of his staff about a skipper
who had mistakenly asked for the bridge to open on the wrong date. He wanted
the bridge to open on Saturday. Stevens said: ‘He’s giving 24 hours notice.
We will have to change that and get the bridge lifted.’ He joked: ‘Tell
him I’m owed at least a pint.’