The name Roussillon is derived from Ruscino (Rosceliona, Castel Rossello), a small fortified place near modern-day Perpignan where Gaulish chieftains met to consider Hannibal's request for a conference.

In 792, the Saracens again invaded France, but they were repulsed by Count Guillaume of Toulouse – regent of the child Louis the Pious, King of Aquitaine – whose hegemony extended into Catalonia.

Under the Aragonese monarchs, economic and demographic growth of the region continued, and Collioure (Catalan: Cotlliure), the port of Perpignan, became an important locus of Mediterranean trade.

[citation needed] As the French and Aragonese crowns grew in power, the region of Roussillon, forming part of the border between them, was frequently a site of military conflict.

By the Treaty of Corbeil (1258), Louis IX of France formally surrendered his claims of sovereignty over Roussillon and to the title of Count of Barcelona to the Crown of Aragon, recognizing a centuries-old reality.

[citation needed] James I of Aragon had wrested the Balearic Isles from the Moors and joined these islands with Roussillon to create the Kingdom of Majorca, with its capital at Perpignan.

Lacking the resources to continue the struggle, James then became reconciled to his brother Peter, and in 1311 the former was succeeded by his son Sanç I, or Sancho I, who founded the cathedral of Perpignan shortly before his death in 1324.

The province, having been pledged as collateral to Louis for 300,000 crowns, was occupied by French troops until 1493, when Charles VIII evacuated the region as part of a settlement with Ferdinand the Catholic (son of John II of Aragon).

Eventually the Spanish, under personal command of Ferdinand, not only secured Roussillon but managed to push into southern France before the new French monarch, Louis XII, signed the Treaty of Granada (1500).