Between 1825 and 1840, Marc Isambard Brunel built the first tunnel under the River Thames from Wapping to Rotherhithe. It had been previously thought that this was impossible. The tunnel was dark and could only be accessed through the construction shafts therefore it was bought by the East London Railway company in 1865. It later became part of the Metropolitan Railway. Thus, Brunel constructed the oldest part of the London Underground 20 years before the opening of the Metropolitan line between Paddington and Farringdon Street.
In order to construct the tunnel he needed to create a tunneling shield, which he did alongside Thomas Cochrane, 10th Earl of Dundonald. The first shield was divided into small sections so that workers could safely dig at the dangerously unstable rock ahead of them. Nonetheless, the shield was rectangular in shape and therefore it was prone to collapse because of instability in certain places.
This tunneling shield was greatly improved in 1970 by civil engineers Peter W. Barlow and James Henry Greathead when they constructed the world’s first deep-level tube.