Reminds me of
Neuf-Brisach, in France, just over the border from
Breisach, in Germany. The French were told they had to let Germany (Then the Holy Roman Empire) have the original Breisach in the Treaty of Ryswick... in 1697.
Incidentally, both towns are worth a visit: The German one is an old city surrounding a castle on a high hill in the plain, and the French one is an almost perfect star fortress.