William the Conqueror built many castles after invading England in 1066, starting with one where he landed in Pevensey. Early castles like motte-and-bailey designs were quick to build but mainly made of wood, making them vulnerable to fire attacks. As motte-and-bailey castles kept burning down, stone keeps were developed that were more resistant to fire. Towers were added to castles for additional defense and protection. Over time, castles evolved from early wooden structures to traditional stone designs with large stone towers for protection.