William the Conqueror chose the site for Windsor Castle, high above the River Thames and on the edge of a Saxon hunting ground. He began building at Windsor around 1070, and 16 years later the Castle was complete. The Castle was originally constructed to guard the western approach to London.

Following his victory at the Battle of Hastings in 1066, William the Conqueror embarked on a massive castle-building program to solidify his rule over England, the most significant of which is the White Tower, the central keep of the Tower of London. Constructed starting in the 1070s, it was designed to be a terrifying symbol of Norman power and a secure fortress against potential uprisings from the citizens of London. It was built using white stone imported from Caen, France, which made it stand out starkly against the timber buildings of the era. Beyond the Tower of London, William was responsible for the foundation of Windsor Castle, which remains the oldest and largest occupied castle in the world today. He also commissioned Battle Abbey on the site of his victory in East Sussex as a penance for the lives lost during the conquest. These stone structures represented a fundamental shift in English architecture, moving away from Anglo-Saxon wood fortifications toward the permanent, imposing stone masonry that would define the English landscape for centuries to come.