Town Walls commenced by Edward I, with no remains for that period, and then completely remodelled for artillery defence with angle Earthen and stone rampart from 1558 onwards. The Elizabethan ramparts with their bastions, gateways and earthworks survive. Spades Mire is an earthwork linear ditches, possibly forming an outer line of defence for medieval Berwick. Evidence suggests that the earthwork is earlier than the late C13 and early C14 defences of Berwick upon Tweed. The earthwork survives as a pronounced linear ditch 672m long ranging from 10m to 25m wide and from 0.9m to 3m deep. Situated on the south side of the ditch are traces of an accompanying rampart, now much spread and up to 13m wide. The earlier works culminated in the original mediaeval walls, their modifications, and the creation of a citadel between the Great Bulwark and St Nicholas's Tower on the East side of the town. This was to built high enough to command the castle, and was to incorporate 4 angle bastions also mounting artillery. Although constructed, the new modifications to Berwick were inadequate for the all round task of providing defence for the town, and it was realised that a radical solution was required, culminating in the Italianate bastioned trace defences of the Elizabethan period.
The Lord's Mount is a massive curved stone bulwark which was built in the 1540s to protect the town walls at their weakest point. An earth bulwark had been built in front of the medieval bell tower in 1522, overlooking the long bank and ditch in the fields to the north of the walls, later recut and known as 'Spades Mire'. By 1539, however, the bulwark needed to "be made smaller so that fewer men could guard...where the walls were weakest". The construction of Lord's Mount marked a small but significant step in the development of military architecture. It has six vaulted gun casements, each with expense magazines in the side walls, and smoke vents