Windsor Castle is the oldest and largest occupied castle in the world. It is open to visitors throughout the year. Founded by William the Conqueror in the 11th century, it has since been the home of 40 monarchs. Windsor Castle is a royal residence at Windsor in the English county of Berkshire, about 25 miles (40 km) west of central London. It is strongly associated with the English and succeeding British royal family, and embodies almost a millennium of architectural history. The original castle was built in the 11th century, after the Norman invasion of England by William the Conqueror. Since the time of Henry I (who reigned 1100–1135), it has been used by the reigning monarch and is the longest-occupied palace in Europe.