The northern supr earthworks, Spur redan and associated tunnels which linked this area and St. Johns tower to the northern entrance, were originally constructed in the 13th century after the 1216 siege, but were very different to was is visible today. The spur as it is today is mainly of an 18th century date; it was remodelled in the 1750’s and then again in the 1790’s. Now the Spur Redan comprises a great earthwork in the shape of a barbed arrowhead, projecting to the north and a redan (a raised gun battery) within this with brick revetted ditch immediately in front of it sunken into the spur. The redan is raised c.3 - 3.5 m above the main ground level of the spur and the base of the ditch is a similar depth below it. (location accurate to the nearest 1m based on available information)