Tunneling Under the River Thames
London has a high number of river tunnels because, historically, the city center has relatively few railway bridges. There are only three railway bridges in central London, only one of which provides services across the river. For this reason, railway builders have had to tunnel under the river in the city center rather than bridge it. In contrast, there are many railway bridges to the west of the inner city.
This unequal spacing of bridges was mainly a result of The Port of London. The Port of London lies along the banks of the River Thames from London to the North Sea. It was once the largest port in the world; and is currently the UK’s second largest port. It is not located in one area but stretches along the Thames, including central London, and has many wharfs, docks, terminals and facilities built over the centuries. This port required large ships to be able to access the river as far upstream as the City of London until the 1980s. Technology had not evolved enough to engineer high bridges that could support trains until the late 1900s. Therefore railways had to be built in tunnels to cross the central and east parts of the city. Additionally, the width of the river downstream meant that tunnels were the only option for crossing before the improvement of technology allowed the construction of high bridges.