In 2012, Margaret and Bernard Shaw took Berwick-on-Tweed to the very edge of Russia. In Narva, Estonia they compared the two walled border towns. Their paper, which was published by Narva will be linked here when I can get an electronic version. Here is the presentation that they gave in Narva with its extensive illustrations.
The Bridges make the town - the fortifications keep both safe.
More about the Royal Border bridge is linked here.
Further notes about Narva and Berwick will be added soon and you are also invited to visit the website of the Narva Museum