AAt the beginning of the 19th century, the port of London was the busiest in the world. Cargoes that had travelled thousands of miles and survived all the hazards of the sea were unloaded on the banks of the Thames, only for their owners to discover that the most frustrating portion of their journey lay ahead. Consignments intended for the southern parts of Britain had to be lifted onto horse carts, pulled through the docks and across London Bridge, built in the 12th century and impractical as its early date implies. By 1820, London Bridge had become the centre of the world’s greatest traffic jam.

BIt was an intolerable situation, and it was clear that if private enterprise could build another crossing closer to the docks, there would be good money to be made in tolls paid by users. Another bridge was out of the question, as this would deny sailing ships access to the city centre, and ambitious men turned their thoughts to tunnelling beneath the Thames instead. This was not such an obvious idea as it might appear. Although increasing demand for coal had meant a great many tunnels had been dug in mines in Britain, working methods remained primitive. Tunnels were dug by men with simple tools, by candlelight. However, in 1807, a group of businessmen got themselves up as the Thames Archway Company. Their ambition was to tunnel below the Thames, but there was little to guide them as there had been no previous attempt to do this. Their chief engineer was Richard Trevithick, designer of the world’s first high-pressure steam engine. His men made progress at the beginning, but then things began to go disastrously wrong, with muddy soil pouring into the tunnel. Eventually the Thames Archway Company had had enough. Its funds were exhausted, Trevithick was sick from exposure to the river water, and its efforts had proved only that a passage under the river exceeded the limits of contemporary mining technology.

CAt that time, the only machines used in mines were pumps. It took a man of genius to recognise that a different sort of machine was needed, a machine that could prevent the roof and walls of a tunnel from collapsing. This man was Marc Brunel, a Frenchman who had become one of the most prominent engineers in Britain. Not long after the failure of the Thames Archway Company, Brunel saw a rotten piece of wood lying on the river bank. Examining the wood through a magnifying glass, he observed it was infested with something that looked like a worm. Brunel realised that as it tunnelled through the wood, it would push chewed wood into its mouth and digest it, then excrete a hard substance that lined the new tunnel. Brunel realised that the worm’s digging technique could be adapted to produce a new way of tunnelling. His realisation led him to invent a device that has been used in one form or another in most major tunnels since: the tunnelling shield. It consisted of a series of iron frames that could be pressed against the tunnel face and supported on a set of horizontal wooden planks that would prevent the face from collapsing. It was a complex machine and not easy to use, but it seemed that it would protect the miners. Brunel’s team examined the sands taken from beneath the riverbed, and subsequently decided to dig the tunnel close to the muddy river bottom, where he could expect to find clay. This would be a more solid and safe substance to dig through than the sand that was found deeper down.

DBrunel began work on his tunnel in 1825, but the problems of such an operation soon became apparent. Although the shield itself worked well, water began to drip into the tunnel. This was more of an annoyance than a danger while the pump was working, but this machine proved unreliable and sometimes failed altogether, meaning that floods began to occur with increasing regularity. The miners often had to run for their lives. Even when Brunel’s men were able to work, they complained of frequent headaches, because the air underground was dirty and contaminated due to the lack of an adequate ventilation system. There were other problems too. Illuminating the tunnels was a constant challenge. Lamps gave off only a weak glow, and there were a number of accidents because the miners could not see what they were doing. Lastly, a number of Brunel’s miners walked off the job because they could not tolerate the excessive temperatures that developed in the cramped conditions underground.

EDespite all the setbacks, the tunnel finally emerged on the opposite river bank on August 12, 1841. Brunel’s triumph, however, was only partial. The small payment of a penny per person made by the thousands of visitors hardly paid the interest on the government loan he had required to complete the project. As a result, there was never enough funding to make it accessible to horse-drawn vehicles, as intended. Instead, the passageways were filled with souvenir-sellers by day and the homeless at night, before it was finally closed.

FIt was only when the underground railway came to London in the 1860s that the Thames Tunnel achieved a measure of real usefulness. It was bought in 1869 by the East London Railway, who found it to be in such excellent condition that it was immediately pressed into service as a passage for passenger trains heading east. The tunnel became, and remains, part of the London Underground network.