Commemorative trowel used to lay the first stone of the Thames Tunnel, 1825.

UNITED KINGDOM - OCTOBER 09: Trowel used by William Smith MP, Chairman of the Thames Tunnel Company, to lay the first stone on 2 March 1825. Sir Marc Isambard Brunel (1769-1849) was at the forefront of civil engineering and his most remarkable undertaking was the Thames Tunnel from Rotherhithe to Wapping, for which he used the tunnelling shield he patented in 1818. This was a large iron box divided into 36 separate cells, each containing a single worker who dug at the face in front of them. The shield was pushed forward through the soft clay as digging progressed and the tunnel was lined with bricks. Construction began in 1825, but was not completed until 1843, partly due to the workings being totally flooded in 1828, causing the project to be abandoned for several years. 50,000 people walked through the tunnel on the day it opened. (Photo by SSPL/Getty Images)