Less than six kilometers before river Bidasoa, near the French-Spanish border, empties into the Atlantic Ocean, there lies a small river island called Pheasant. It was here, in 1659, that representatives from France and Spain met and signed the Treaty of the Pyrenees, officially ending the Thirty Years War. The treaty also drew a new border that runs along the Pyrenees mountains, and then follows the Bidasoa river to the Bay of Biscay in the Atlantic Ocean,  forming a natural border between France and Spain. As is usually the case with borders that follow the course of a river, the French-Spanish border was fixed along the center of the river. Ideally, the border should have cut right through Pheasant Island splitting the 1.6 acre island into two halves, with France and Spain controlling their respective sides. But the Treaty of the Pyrenees agreed upon a different kind of arrangement, by which Pheasant Island became a condominium.

Pheasant Island (Isla de los Faisanes, in Spanish, and Île des Faisans, in French, as seen from the Spanish side. Photo credit: Zarateman/Wikimedia