Windsor Castle, in Berkshire, the largest occupied in the world, has belonged continuously to the sovereigns of England since the days of the Norman Conquest over 900 years ago.

Originated as a motte and bailey fortification (an earthwork surmounted by wooden palisades), Windsor was one of a ring of garrisons built by William the Conqueror (1066-1087) to command the area around London, each a day's march from its neighbors and from the center. Built on the only naturally defensive site on a ridge above the Thames Valley, the site at Windsor was of strategic importance because it dominated the Thames, the main freight route to the interior.

The site was at the edge of a vast tract of royal forest in which the Saxon kings had hunted for centuries, with a small hunting lodge four miles downstream, in an ancient settlement called Windlesora. The Norman invaders also enjoyed the hunt and named the new fortress after it.