When in 1659 the Treaty of the Pyrenees was signed, it ended the conflict between France and Spain, which had been continuing since the Thirty Years' War. The borders between the Pyrenees were drawn anew; among other things, the Roussillon came under French rule. Another part of the contract was the marriage of a Spanish princess with Louis XIV. This was supposed to stabilize the peace agreement, but eventually led to another conflict: Due to this marriage, the French monarchy gained a claim to the Spanish throne. After the Spanish line of the House of Habsburg had ceased to exist, this claim became one of the causes of the War of the Spanish Succession.
Nicolas Sanson (1600–1667), Les monts Pyrénées, où sont remarqués les passages de France en Espagne, map, between 1692 and 1695; source: Jaillot, Hubert: Atlas françois, compilation des cartes de Nicolas Sanson, Paris et al. 1692–1695, Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Carte_des_Pyr%C3%A9n%C3%A9es_au_XVIIeme_si%C3%A8cle.jpg?uselang=de, public domain.