Historically and architecturally, kings have lived in both castles and palaces, but the choice depends on the era and the primary purpose of the residence. A castle is a fortified structure built during the Middle Ages designed for defense; it served as both a military stronghold and a private home for royalty or nobility. When a king lived in a castle, it was because he needed protection from invaders or local uprisings. As warfare evolved and the need for thick stone walls and moats diminished with the advent of gunpowder, royalty moved into palaces. A palace is a grand, unfortified residence whose primary purpose is to display wealth, power, and artistic splendor rather than provide a defense. For example, Windsor Castle is a royal residence that retains its medieval fortifications, while the Palace of Versailles was built purely for luxury and courtly life. Today, most modern monarchs live in palaces (like Buckingham Palace), though they may maintain historic castles for ceremonial purposes or as summer retreats. Essentially, you live in a castle if you're worried about being attacked, and you live in a palace if you want everyone to know how rich you are.