Briefly, Edward I initiated the building of a set of walls similar to those at Conwy and Caernarfon after attacking Berwick in March 1296. They were modified over the years. Lord’s Mount is a large circular gun emplacement built in the 1540s in the north-east corner of the walls. (Henry VIII added two more smaller gun towers to the castle.)
Megs Mount, Cumberland Bastion, Brass Bastion, Windmill Bastion and Kings Mount are all part of the Elizabethan ramparts built between 1558 and 1570. They are huge arrow-shaped bulwarks attached to the curtain walls and designed such that all faces of the walls and Kings Mount was meant to be joined directly to Megs Mount but the project overran budgets and the original motivation for the building dissipated.
Aerial view of Berwick showing the bastioned fortifications. Brass Bastion is in the foreground.
In the end, the scheme was never finished. Kings Mount in the south-east was meant to connect directly with Megs in the north-west but to save money and time, these bastions were connected to the earlier walls that run around the riverside.
Among the towers here and one of only here that survive, is Coxon’s Tower. This was probably not built until the early 14th century. It was modified in the late 15th century by the addition of a “stone bulwark” a gun platform projecting into the river and again in the mid-18th century when these riverside walls were thickened by the Georgians. The original Coxon’s Tower was encased within 2m of masonry.
I hope that helps. If you need anything more specific, please let me know and I might do a full blog piece about it. I am writing a book on the subject though I have no idea when it will be finished!