Conisbrough Castle is an 11th century earthwork motte and bailey fortress, founded by William de Warenne. The enormous motte, which supports the inner bailey, is a natural mound, strongly scarped and ditched. In the 12th century, Hamelin de Plantagenet founded the stone castle, when adding the unique cylindrical buttressed keep. A high inner bailey curtain wall, flanked with solid circular towers, encases the keep and the foundations of various 13th century, domestic buildings. Beyond the fallen gatehouse, with its flanking angled barbican, is a curved outer bailey. By the 16th century, the castle was suffering from neglect and one floor of the keep, the bridge, its timber and stonework gates, and part of the curtain wall had all fallen. 2 miles north-west at Mexborough is Castle Hill and 7 miles south-east is Tickhill Castle.