Old Mulgrave Castle is an early 13th century stone enclosure fortress, founded by Peter de Maulay. Standing on a high ridge and encased by ditches is a large flat irregular polygonal enclosure. With baileys to the west and east, this successor to Foss Castle was mentioned as ruinous in 1309. The encasing curtain wall is now only a buttressed revetment but it's still flanked by rectangular towers and a western gatehouse with solid semi-circular towers. Near the centre of the enclosure are the remains of an early 14th century square keep, that was once surrounded by ranges of buildings. The keep was altered in the late 16th century but the lower parts of the north and south walls may date to the 13th century. Garrisoned by Royalists troops during the Civil War, the castle slighted by order of Parliament in 1647.