William, Duke of Normandy, invaded England in 1066 and one of his first actions after landing was to build Hastings Castle to protect his supply routes. Following their victory at the battle of Hastings the Normans began three phases of castle building. The first of these was the establishment, by the new king, of a number of royal castles in key strategic locations. This royal castle programme focused on controlling the towns and cities of England and the associated lines of communication, including Cambridge, Huntingdon, Lincoln, Norwich, Nottingham, Wallingford, Warwick and York. Of the castles built by William the Conqueror two-thirds were built in towns and cities, often those with the former Anglo-Saxon mints. These urban castles could make use of the existing town's walls and fortifications, but typically required the demolition of local houses to make space for them. This could cause extensive damage, and records suggest that in Lincoln 166 houses were destroyed, with 113 in Norwich and 27 in Cambridge. Some of these castles were deliberately built on top of important local buildings, such as the "burhs" or halls of local nobles, and might be constructed so as to imitate aspects of the previous buildings – such as the gatehouse at Rougemont Castle in Exeter, which closely resembled the previous Anglo-Saxon "burh" tower – this was probably done to demonstrate to the local population that they now answered to their new Norman rulers.