tunnel designed by Marc Isambard Brunel (Brunel, Sir Marc Isambard) and built under the River Thames (Thames, River) in London. Drilled from Rotherhithe (in the borough of Southwark) to Wapping (now in Tower Hamlets), it was the first subaqueous tunnel in the world and was for many years the largest soft-ground tunnel. To drive his heading, Brunel invented the tunneling shield, one of the basic tools of modern civil engineering. The tunnel was completed in 1843 but was used only for pedestrian traffic until the 1860s, when it was converted to railway use. It originally measured 1,200 feet (366 metres) in length; its cross section measured 22.25 by 37.5 feet (7 by 11 metres). The tunnel has been in use as part of the London Underground (Tube, or subway) since 1913. It underwent refurbishment in the late 1990s.