The Thames Tunnel is a tunnel built beneath the River Thames in London, connecting Rotherhithe and Wapping. It measures 11 m wide by 6m high and is 396 m long, running at a depth of 23m. It was the first tunnel constructed successfully underneath a navigable river and was built using Marc Isambard Brunel's newly invented tunnelling shield technology.

In 1823-4 Brunel produced the plan; financing was found from private investors and a Thames Tunnel Company was formed. The project began in February 1825. When the resident engineer fell ill in 1826 Marc's son Isambard Kingdom Brunel took over at the age of 20.

Work was slow and hazardous. The tunnel flooded in May 1827 and in January 1828. Financial problems followed, leading to the tunnel being walled off and abandoned for seven years. In December 1834 Marc Brunel succeeded in raising money to continue construction.

The tunnel finally opened to the public on 25 March 1843.

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