A strong quadrilateral moated site, near the present manor house. The ditch is 25 feet deep and there is a massive inner bank. There is no trace of masonry. {1} A strong defensive earthwork, probably of the English Civil War period. Similar sites have been investigated in the Newark, Nottinghamshire area and at Welbeck Hill in this county. {2} In 1086 land at Withern was held by Earl Hugh as part of his manor at Greetham, and between the 13th and 15th centuries it was variously held by the Well family and the Crown. From the 15th to the 18th centuries, a branch of the Fitzwilliam family, established at Mablethorpe Hall, held large estates in Withern and Mablethorpe; 17th century documentary evidence makes reference to Fitzwilliams at Withern, and Castle Hill is believed to have been the location of a house belonging to the Fitzwilliam family. In the post-medieval period a building known as Withern Hall was located immediately to the north-west of the site but was later destroyed. {3} Although medieval in origin, the moated site is believed to have been altered in the post-medieval period to form a defensive position which included the creation of ramparts and bastions, together with the enhancement of the moat. During the Civil War, the area around Withern was garrisoned by the Parliamentarians, including Mablethorpe Hall; these positions were captured by the Royalists in the summer of 1643 and were then retaken by Parliamentarian forces, although subsequently raids continued to be made in the area. The alterations to the moated site would have provided defences overlooking the approaches to the site and the nearby church. The north-western side of the monument, where the rampart is absent, would have been afforded protection by the low-lying ground between the monument and the river, an area prone to flooding. {3} All fences are excluded from the scheduling, although the ground beneath them is included. {3}