The Pyrenees are a range of mountains in southwest Europe that form a natural border between France and Spain. The semi-autonomous state of Andorra is in this range. They separate the Iberian Peninsula from the rest of continental Europe, and extend for about 430 km (267 mi) from the Bay of Biscay to the Mediterranean Sea.
When the Roman Empire recovered Ispania from the Visigoths, its armies drove the barbarians back to the Pyrenees mountains. These formed a natural barrier and so the Empire constructed a series of fortresses to guard the passes from Visigoth and later Franco-Saxon invasions.