Berwick was fought over and changed hands thirteen times, 

In 1296  'Edward the first' of England arrived and tried to conquer Scotland.  The three hundred years of conflict that  followed turned the area into an armed frontier zone that stretched for sixty miles south of the Tweed. 

As a result the area is rich in castles and historic buildings

The defensive wall was a major undertaking. 
It took two thousand men ten  years to build it and more was spent in constructing this defense against the Scots that was spent on defeating the Spanish Armada.  

The great earth ramparts were never to be attacked, they were finished just in time for the Union of the Crowns, and instead they became part of the country's coastal defenses. 

News of any approaching threat from French or Spanish ships could be signalled with flaming beacons. Warning fires lit around the coast from the Lizard in Cornwall would take only fifty minutes before being sighted at Berwick
.

The Guard House was rebuilt in Palace Green in 1815

Once a large seaport,  Berwick-upon-Tweed grew on the trade with barley., (the name Berwick comes from ‘beil wick’ which means ‘Barley Farm.’) 

There was also the salmon fishing and the wool trade,  so merchants were attracted from all over Europe and Flemish, German and Scandinavian traders set up businesses in the town