Her Majesty's Royal Palace and Fortress, known as the Tower of London, is a historic castle located on the north bank of the River Thames in central London.
It was founded towards the end of 1066 as part of the Norman Conquest of England. The White Tower, which gives the entire castle its name, was built by William the Conqueror in 1078, and was a resented symbol of oppression, inflicted upon London by the new ruling elite.
The castle was used as a prison from 1100 until 1952 althought that was not its primary purpose. There was a great deal of expansion in the 12th and 13th centuries. It is a World Heritage Site.
The main building material is rag-stone from Kent. Caen stone was imported from Normandy to provide details in the Tower's facing. Much of the Caen stone was later replaced with Portland stone in the 17th and 18th centuries.

Tower of London
London, England
Photograph by Rafa Esteve