Windsor Castle in Berkshire England was started by William the Conqueror in the 11th century. It has been used by the reigning monarch and is the longest-occupied palace in Europe. Originally designed to project Norman dominance around the outskirts of London and oversee a strategically important part of the River Thames, Windsor Castle was built with three wards surrounding a central mound. Windsor Castle grounds cover 13 acres (52,609 square metres) and combines the features of a fortification, a palace, and a small town. Consisting of Upper, Middle and Lower Wards, State Apartments, Parks and Gardens, Windsor Castle has undergone many changes through the centuries and remains one of the world's most-visited sites.