Ferdinand III, called “The Saint,” became King of Castile in 1217 when his mother, Berengaria, renounced her title to the Castilian throne in his favor. He became King of Leon in 1230.

Alfonso, Ferdinand’s father, who had himself expected to acquire Castile, was angered at his wife’s action, and, aided by a group of Castilian nobles favorable to his claim, made war upon his newly crowned son. Ferdinand, however, with the wise cousel of his mother, proved more than a military match fo Alfonso, who at length was forced to abandon his plan of conquering Castile. Through the good offices of Berengaria, Ferdinand was able to effect the peaceful union of Leon and Castile upon the death of his father in 1230. Ferdinand devoted his energies to prosecuting the war against the Moors, conquering Cordoba in 1236 and Seville in 1248. He was rigorous in his suppression of the heretical Albigenses, a fact largely responsible for his canonization more than two centuries later. In 1242, Ferdinand reestablished at Salamanca the university originally founded by his frandfather.