Ferdinand III permanently united Castile and León and conquered most of al-Andalus — Córdoba, Jaén, and Seville — leaving only Granada as an independent Muslim state; he was later canonised as San Fernando.
Ferdinand III ruled Castile from 1217 and León from 1230, and by joining the two crowns permanently he created the dominant Christian power of Iberia. He then led the greatest surge of the Reconquista, conquering the heartland of al-Andalus.
In little more than a decade he took Córdoba (1236), Jaén (1246) and Seville (1248), and reduced Murcia and Granada to tributary status. By his death in 1252 only Granada survived as an independent Muslim state. He was canonised in 1671 as San Fernando.
Ferdinand came to the throne of Castile in 1217 when his mother Berengaria, who had inherited it, stepped aside in his favour. In 1230, on the death of his father Alfonso IX of León, he claimed and secured León as well, ending the recurring separation of the two kingdoms.
With the Almohad order collapsing after Las Navas de Tolosa, he drove south down the Guadalquivir. Córdoba fell in 1236 and Seville, after a siege broken by a river fleet, in 1248. He organised the resettlement of the conquered cities and the great military orders that held the frontier, and he died at Seville, where he is buried in the cathedral.
Ferdinand was remembered by his own court and by later tradition as the model of a Christian warrior-king: pious, just, and relentless in the holy war of reconquest, a reputation that carried him to sainthood four centuries after his death. The chronicles stress his devotion and his care to give his conquests a religious frame.
Behind the saintly image was an effective and hard-headed ruler. He managed the difficult union of Castile and León, worked closely with the military orders and the Church, and organised the settlement of vast new territories — the administrative labour that made his conquests permanent rather than passing raids.