Historians estimate that King William the Conqueror commissioned or directly oversaw the building of around 84 to 100 castles across England during his reign from 1066 to 1087. Following his victory at the Battle of Hastings, William used a "castle-building blitz" as a primary tool for psychological warfare and military control over a rebellious Anglo-Saxon population. Most of these initial structures were motte-and-bailey castles—quick-to-build wooden fortifications atop a raised earth mound. Over time, these were replaced or supplemented by massive stone keeps that served as permanent symbols of Norman authority. The most famous of his legacy includes the Tower of London (specifically the White Tower), which was built to overawe the citizens of London, and Windsor Castle, which remains the oldest and largest inhabited castle in the world. Other strategically placed strongholds like Dover Castle, Warwick Castle, and Colchester Castle were part of this massive defensive network designed to secure key trade routes and borders against both internal uprisings and external threats like Viking raids.