Tower of London, a 900-year-old fortress in London, England, now used as a museum. The 18-acre (7.3-hectare) fortress, consisting of a number of buildings enclosed by a double wall and a moat, is on the north bank of the Thames. In the past it has been a royal residence and a prison for many high-ranking figures, and has at various times housed the royal mint, the public records, the royal armories, the royal observatory, and the royal menagerie. In vaults in the Waterloo Barracks are displayed the British crown jewels.

The Tower of London takes its name from its oldest building, the White Tower, which today is used to exhibit historic weapons and armor. Nineteen smaller towers are built into the walls of the fortress. The walls of the Beauchamp Tower bear a number of inscriptions carved centuries ago by prisoners. The Bloody Tower received its name because it was believed that the boy king Edward V and his brother were murdered here.

Beneath St. Thomas's Tower is Traitor's Gate, through which many prisoners entered the fortress, including Sir Thomas More, Princess Elizabeth (later Queen Elizabeth I), and Lady Jane Grey. Executions were carried out either on Tower Hill, northwest of the Tower, or on Tower Green, within the walls. The bodies of many executed prisoners, including two wives of Henry VIII, Anne Boleyn and Catherine Howard, lie in the Royal Chapel of St. Peter ad Vincula (St. Peter in Chains).

William the Conqueror began construction of the White Tower about 1078 on the site of some ancient Roman fortifications. The fortress walls were built mostly during the reign of Henry III (1216–72). The Tower was used as one of the royal residences until the end of the 17th century. It was customary for monarchs to stay there on the night before they were to be crowned. The last Tower prisoner was Hitler's associate Rudolf Hess, who was confined there briefly in 1941.