Which country is home to the longest-occupied palace in Europe?

Windsor Castle is a royal residence at Windsor in the English county of Berkshire. It is notable for its long association with the English and later British royal family and for its architecture. 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, it has been used by the reigning monarch and is the longest-occupied palace in Europe.

Originally designed to protect Norman dominance around the outskirts of London and oversee a strategically important part of the River Thames, Windsor Castle was built as a motte-and-bailey, with three wards surrounding a central mound. Gradually replaced with stone fortifications, the castle withstood a prolonged siege during the First Barons' War at the start of the 13th century. Henry III built a luxurious royal palace within the castle during the middle of the century, and Edward III went further, rebuilding the palace to make an even grander set of buildings in what would become "the most expensive secular building project of the entire Middle Ages in England". Edward's core design lasted through the Tudor period, during which Henry VIII and Elizabeth I made increasing use of the castle as a royal court and centre for diplomatic entertainment.