The Tower of London, officially Her Majesty’s Royal Palace and Fortress of the Tower of London, is a historic castle on the north bank of the River Thames in central London. It lies within the London Borough of Tower Hamlets, which is separated from the eastern edge of the square mile of the City of London by the open space known as Tower Hill. It was founded towards the end of 1066 as part of the Norman Conquest. 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 also used as a prison from 1100 until 1952, although that was not its primary purpose. A grand palace early in its history, it served as a royal residence. As a whole, the Tower is a complex of several buildings set within two concentric rings of defensive walls and a moat. There were several phases of expansion, mainly under kings Richard I, Henry III, and Edward I in the 12th and 13th centuries. The general layout established by the late 13th century remains despite later activity on the site.

The Tower of London has played a prominent role in English history. It was besieged several times, and controlling it has been important to controlling the country. The Tower has served variously as an armory, a treasury, a menagerie, the home of the Royal Mint, a public record office, and best known as the home of the Crown Jewels of England (no photographs allowed) and a prison.

In the Middle Ages the Tower of London became a prison and place of execution for politically related crimes, with most captives being put to death on Tower Green or, outside the castle, in public on Tower Hill. Prisoners were generally brought in via the Traitor’s Gate, transported by barge along the Thames, and passing under London Bridge, where the heads of recently executed prisoners were displayed on spikes. Among those killed there were Sir Simon Burley, an adviser and tutor of Richard II; the statesman Edmund Dudley (1510); the humanist Sir Thomas More (1535); the second wife of Henry VIII, Anne Boleyn (1536); Lady Jane Grey and her husband, Lord Guildford Dudley (1554); and the 11th Lord Lovat, Simon Fraser (1747), who was a Scottish Jacobite leader. During World War I several spies were executed there by firing squad. Other notable inmates included Princess Elizabeth (later Elizabeth I), who was briefly imprisoned by Mary I for suspicion of conspiracy; the soldier and conspirator Guy Fawkes; the adventurer Sir Walter Raleigh; and Sir Roger Casement, who was arrested for treason during World War I. In 1483 the adolescent king Edward V and his younger brother were last seen in the Tower before their disappearance and probable murder (great show on PBS about their plight, Lucy Worsley Investigates, Princes in the Tower).

A military garrison is maintained within the Tower.

There is a resident governor, who occupies the 16th-century Queen’s House on Tower Green and is in charge of the yeoman warders, or “beefeaters,” as they are popularly called. They still wear a Tudor uniform and live within the Tower, and their responsibilities include guiding tours for the Tower’s two million to three million annual visitors.

Ravens with clipped wings are kept on the grounds by the yeoman ravenmaster; a tradition dating from the time of King Charles II (reigned 1660–85) states that, should the ravens leave the Tower, the fortification and the state would fall. By the Tower is Tower Bridge (1894), the only central-city bridge across the Thames below London Bridge. The fortress was designated a UNESCO World Heritage site in 1988.