The site of Old Sarum is located one and a half miles north of the present town of Salisbury. Here the Normans built a royal castle within the earthworks of an Iron Age hillfort. During the twelfth century a great tower and palace were built in the inner bailey. The cathedral, begun in the late eleventh century, was constructed on the north side of the outer bailey. The cathedral remained the seat of the bishopric until 1218 when the pope permitted the clergy to remove to a new site.