France: Salses Fortress
Salses Fortress aka Fortresse de Salses was built by Catalans at the end of the 15th century to guard the border between France and Principality of Catalonia. The fortress was built on a strategic point with multiple layers of fortification (very advanced for the time) and around a spiral of water, a useful element in case of a siege. Sales fortress was besieged, captured and recaptured in 1503, 1639, and 1640, before being finally taken by the French in 1642. The Treaty of the Pyrenees redefined the borders in 1659 ceding the territory to the French and making Salses strategically useless. Interestingly, years later the greatest military architect of all times, Vauban, restored the fortress.