A River’s Secret Border
In the middle of the Bidasoa River, between France and Spain, lies a small, uninhabited patch of land that quietly shifts nationality every six months. Pheasant Island, only about 200 meters long, is the world’s smallest condominium. From February to July, it belongs to Spain.
From August to January, it becomes French. No one lives there, no buildings rise from its soil, and access is forbidden except for a handful of officials who cross the shallow water to clean and maintain it.
A Stage for Kings and Treaties
In 1659, this quiet island witnessed one of Europe’s defining diplomatic moments. After decades of war, Spanish grandee Luis Méndez de Haro met France’s Cardinal Mazarin here for twenty-four conferences that led to the Treaty of the Pyrenees.
The agreement ended the long conflict between the two kingdoms. A stone monolith still stands at the center of the island to mark where the treaty was signed.
Royal Meetings and Farewells
The island also hosted royal encounters that shaped dynasties. In 1659, Louis XIV met his future wife, Maria Theresa of Spain, on the island. The following year she returned to bid farewell to her father, King Philip IV, before crossing into France to marry the French monarch.
In 1721, Louis XV came to meet his intended bride, Mariana Victoria of Spain. The union never happened. He married Marie Leszczyńska instead, while Mariana later became Queen of Portugal.
Shared but Empty
By the terms of the 1659 treaty, both nations agreed to share the island forever. Today, the mayors of Irun and Hendaye take turns overseeing it.
Spain’s naval commander in Hondarribia governs from February to July, while a French “viceroy,” the deputy director for the sea and coast of the Atlantic Pyrenees and Landes, takes charge from August to January. Among those who once held that French title was the writer Pierre Loti.
A Vanishing Landmark
Erosion continues to shrink Pheasant Island. The river’s main current passes north of it, placing the entire landmass technically within Spain’s borders.
At low tide, it can sometimes be reached on foot from the Spanish side, though visits are prohibited except for rare heritage events. Every five days, naval officers from both countries land briefly to check and maintain it—a silent ritual that keeps alive one of Europe’s most unusual diplomatic arrangements.
Pheasant Island sits in the Bidasoa River between France and Spain.
Every six months, it quietly changes country.
From February to July it is Spanish.
From August to January it becomes French.
No one lives there, yet both nations care for it as shared ground…🧵👇 pic.twitter.com/lPbYXp6MSI
— Fascinating True Stories (@FascinatingTrue) October 28, 2025