Berwick is famous for its two sets of town walls. The first, of which only fragments remain, was built by Edward II, and was two and a half miles long; the second, which is the glory of Berwick, dates from the early years of Elizabeth, and is a mile and three-quarters in length. The ramparts completely surround the town, and there are only four gates through the walls.

The medieval walls were begun by Edward I; at least the ditch outside was dug by him; the wall was built by Edward II, and strengthened by Bruce about 1320. It had nineteen towers and five gates and in Henry VIII's time was twenty-two feet high. The wall had an earthen embankment behind which was a retaining wall, forming the "Countermore". Entrance to the towers was through the Counter-more by a narrow passage supported by timber.

The old wall began at the Mary Gate where a short road led to the castle. It went to the Bell Tower and along the line of the wall that is still visible to the Brass Mount. The Bell Tower is not the original but an Elizabethan replacement. Its rounded base is medieval. A stone's throw away can be seen Lord Soulis Tower (also called Lord's Mount) which was begun in Edward's reign and finished in that of Mary, 1555. This is the northeast angle of the Edwardian walls. Lord Soulis was a supporter of Bruce, and was appointed Governor of Berwick. He rebelled against the king, was captured and imprisoned. This was the time when Berwick was controlled by Scotland. From the Brass Mount the medieval wall followed close to the line of the Elizabethan Wall except that the Elizabethan Wall did not take in the area of the Ness. After Meg's Mount the Edwardian wall continued to the castle. There was a gap between the Percy Tower and the Mary Gate which was covered by the castle.

When the Elizabethan walls were built guns, not arrows, dominated warfare. They were built on a new Italian system of bastions which had not been tried out in the north. The Berwick bastions were designed by an engineer, Portinari, and probably by Jacopo a Condo, who was certainly consulted. They are designed to give fire cover for every part of the wall. They consist of a platform facing the attacker with an obtuse angle connected to the curtain wall by a narrow collar. The recesses between the platform, collar and wall are called flankers. They contained guns which fired through embrasures. The flankers were accessible by means of tunnels. The wall was ten to twelve feet thick backed by a mound of earth thirty feet thick. Soon after the wall was built the bastions were filled with mounds of earth above the level of the stonework and called "cavaliers". Because of this the bastions were often called "Mounts".

Outside the curtain wall, as well as round the bastions, there was a ditch 200 feet in width, and in the midst of this another ditch twelve feet broad and eight feet deep, kept always full of water originally a sentry walk ran right round the wall but this was later covered to form the present rampart. Guns could be mounted on the slope behind.

In front of the Brass Bastion can be seen the Batardean, a low wall controlling the water in the moat. From the King's Mount the Catwell Wall ran across to Bridge Street (the Edwardian Wall followed the waterside right round). From the King's Mount a round projection shows where the Edwardian Black Watch Tower used to stand.

In the eighteenth century the Catwell Wall was abandoned and fortifications were built along the riverside as far as the old bridge. Fishers Fort contains a gun captured at Sebastopol. Next comes Four Gun Battery (also called Brarriham's Battery) which as its name implies has four stone platforms and embrasures. Coxon's Tower probably incorporates the Edwardian "New Tower".

The fortifications of Berwick were dismantled in 1819.