Berwick’s precarious position meant that whether Scots or English were in control, there were always reasons to establish defences so that that control could be maintained.
The first castle was built here in the 12th Century by the Scots. In England during this era preference was for the ‘Motte & Bailey’ design introduced by the Normans; the main defensive keep built on high (or artificially raised) ground (the motte) for the nobility, with a curtain wall extending outwards to enclose the courtyard and buildings that supported the economic life of the castle (the bailey). In Durham, the bailey enclosed the peninsula that includes the cathedral and the buildings beyond; the heart of the medieval city.
In many cases the defensive “walls” were simple earthworks topped by wooden palisades. I don’t know if this was case or not in Berwick, but whatever was in place was largely ineffectual. Less than fifty years after David’s work the town was in English hands as part of a ransom deal for William I of Scotland who had invaded England only to suffer defeat and capture at Alnwick. Richard I (“Lionheart”) then sold it back to fund his crusading.
In the 14th century Edward I recaptured the town and built two miles of stone walls, though these separated the town and castle. The following year William “Braveheart” Wallace capture the town for the Scots but not the castle. In the ensuing decades this game of ping-pong continued including one occasion where the Scots took the castle with only seven men!
Elizabeth I put a stop to all this nonsense in two distinct ways.
First she built new defensive walls , using designs from Italy and massive earthworks to support them and absorb the impact of artillery. Arrowhead bastions were one of the innovations, allowing gun post to project at the corners and thus provide defensive fire that covered the length of the new walls and the vital river mouth. These walls enclosed a smaller area, leaving the castle completely cut off and irrelevant. For years until the construction of a by-pass to the west, all traffic heading north along the east coast had to pass through one of the Elizabethan gates.
She had good reason to take defence seriously. Having rejected Catholicism, England was the enemy of much of Europe. Calais had been lost to the French with whom Scotland had “the auld alliance” and the Scots had a charismatic leader in Mary.
Ultimately the Elizabethan works were left incomplete as with Mary’s capture and eventual execution the threat subsided and Elizabeth’s second act removed it all together. On her death she appointed James I of England and VI of Scotland as her successor. The union was created, and recently survived a referendum on independence. What future for Berwick if there were to be another vote? For now at least it can still justify Pevsner’s description as “one of the most exciting towns in England”.