Castle Hill, at the west end of the village southwest of the church, is the earthwork remains of a Saxon and Norman ringwork castle. The northern part of the ringwork was excavated in 1960 and 1976. Evidence was found suggesting that the first construction on the site was a timber-framed hall about 80ft long and a detached stone and timber building, probably built in the late 10th century. They seem to have been an Anglo-Saxon manor house and separate kitchen. This was followed by the building of the earthen rampart, which is now rounded but may originally have been a straight-sided pentagon. After the Norman conquest of England in 1066 the original hall was replaced with a stone one about 40ft long and 18ft wide. Small timber buildings were also added. The earthen ramparts were increased in height in the middle of the 11th century, and again early in the 12th century. The site seems to have been abandoned about 1140. It is a scheduled monument. After the Norman Conquest Sulgrave was one of the manors granted to Ghilo or Gilo, brother of Ansculf de Picquigny. The Domesday Book of 1086 records that three tenants; Hugh, Landric and Othbert; held Sulgrave of him. In the 12th century the manor of "Solegrave" was still in the fee of Gilo. On both occasions the manor was assessed at four hides. In the middle of the 12th century the manor was granted to the Cluniac Priory of St Andrew at Northampton, and the ringwork site was abandoned as a manorial seat.