Which mountain range forms a natural border between France and Spain?

The Pyrenees is a range of mountains in southwest Europe that forms a natural border between Spain and France. Reaching a height of 3,404 metres (11,168 ft) altitude at the peak of Aneto, the range separates the Iberian Peninsula from the rest of continental Europe, and extends for about 491 km (305 mi) from the Bay of Biscay (Cap Higuer) to the Mediterranean Sea (Cap de Creus).

For the most part, the main crest forms a divide between Spain and France, with the microstate of Andorra sandwiched in between. The Principality of Catalonia alongside with the Kingdom of Aragon in the Crown of Aragon, Occitania and the Kingdom of Navarre have historically extended on both sides of the mountain range, with smaller northern portions now in France and larger southern parts now in Spain.