It separates the two countries from Hendaye and Irun in the west, running through the Pyrenees to Cerbère and Portbou on the Mediterranean Sea.

[2] The formal layout of the Franco-Spanish border dates back to the signing of the Treaty of the Pyrenees between the kingdoms of Spain and France in 1659.

Later there were some further agreements covering specific areas: The final definition, which for the most part is still in force, is set out in the Bayonne Treaties between 1856 and 1868.

[clarification needed] In 1980 an agreement was signed to define the border into[clarification needed] the Bielsa-Aragnouet tunnel,[6] and 1984, during the construction of the road linking the Roncal Valley with Arette, a mutual transfer of land of 2710 m2 (29,170 sq ft) was agreed.

Following the provisions of the treaties of Bayonne, the border is physically marked on the ground by 602 cairns showing the division between the two countries.