A prison and place of execution, the Tower of London was also a royal palace, an armoury, a treasury, an observatory, a mint and even a zoo. Cromwell demolished the palace, the observatory went to Greenwich in 1675, the Royal Mint moved out in 1810, and the Victorians moved the zoo. The Tower is a national treasure with a chilling history of suffering and deaths that have taken place within its walls. Originally the site of a Saxon fort William the Conqueror built the White Tower to protect London and to instil fear in his subjects. Over the centuries more walls and towers were added to provide a maze of passageways, dark cells and secret tunnels. The last prisoner to be held at the Tower was Hitler's deputy, Rudolf Hess, in 1941.