Bidasoa bēˈdäsōä, Span. bēᵺäsōˈä [key] or Bidassoa, river, 35 mi (56 km) long, Basque Country, N Spain, and Pyrénées Atlantiques dept., SW France. The river rises in Spain on the southern slopes of the western Pyrenees in Navarre and flows NNW to the Bay of Biscay, entering it between Hondarribia, or Fuenterrabía, Spain, and Hendaye, France. The Bidasoa forms the French-Spanish border for more than 10 mi (16 km) of its lower course. On the small Pheasant Island, located midstream 2 mi (3.2 km) above Hendaye, France and Spain signed (1659) the Peace of the Pyrenees (see Pyrenees, Peace of the), which ended the conflict that had continued between them after the Thirty Years War. Pheasant Island then became permanent neutral territory, with sovereigny shared alternately between the two nations.

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