Canterbury Castle is one of three Norman-built fortifications established by William the Conqueror to consolidate his authority in the region following his victory at the Battle of Hastings in 1066. The surviving keep ruins were constructed early in the 12th century, during the reign of Henry I, making it one of the oldest in Britain. The castle was ultimately overshadowed by a more prominent fortification at nearby Dover. By the 17th century it had become a complete ruin.