The constables tower, located on the south western side of the outer curtain at Dover Castle was constructed in the 1220s to replace the northern gateway. It originally consisted of a D shaped tower which was constructed during the reign of King John (1199-1216) but was modified after the siege of 1216 to form a heavily fortified gateway which was protected by the outer moat and a drawbridge which linked with a stone causeway. In addition to its function as a fortified gate, it was also the official residence of the General Commanding Officer/Deputy Constable it has had a domestic and ceremonial function for many years. (location accurate to the nearest 1m based on available information)