King of Castile and León (1312–1350), who restored royal power after a turbulent minority and crushed the last great Marinid invasion at the Battle of Río Salado.
Alfonso XI, called "the Avenger" or "the Just", was king of Castile and León from 1312 to 1350. He succeeded as an infant of one, and his long minority was a period of anarchy, as rival regents and great nobles fought over the kingdom. Coming into his own power in the mid-1320s, he set about restoring the authority of the crown with a hard hand.
His reign is remembered above all for his triumphs on the Reconquista frontier. In 1340 he crushed a great invasion by the Marinids of Morocco and the emir of Granada at the Battle of Río Salado — the last major Muslim invasion of Iberia — and went on to take Algeciras. He strengthened royal law and government at home, and died in 1350 of the Black Death while besieging Gibraltar.
Alfonso was born in 1311, the son of Ferdinand IV of Castile, and became king in 1312 as a baby of one on his father's sudden death. His minority lasted well over a decade and was among the most turbulent in Castilian history, as his grandmother María de Molina, his uncles, and the great noble factions struggled for control of the regency and plundered the kingdom.
Declared of age in the mid-1320s, Alfonso moved swiftly and ruthlessly to break the power of the overmighty magnates and take the government into his own hands.
Alfonso XI was a hard, forceful, and effective king — a ruler of fierce energy and few scruples, who earned both his bynames, "the Avenger" and "the Just", by the harshness with which he enforced royal authority. Having grown up amid the chaos of his minority, he was determined never to be a puppet, and he crushed the great nobles who had preyed on the kingdom, sometimes by treachery and violence.
That ruthlessness served a genuine vision of strong monarchy. He reformed the law and the administration, curbed the aristocracy, and threw the concentrated power of the crown into the holy war against the Muslims of the south. His private life was as forceful as his public one — his long devotion to his mistress Leonor de Guzmán, and the brood of illegitimate sons she bore him, would ignite a civil war after his death. He is remembered as a formidable warrior-king who restored Castile's strength at home and its fortunes on the frontier.
Once in command, Alfonso XI rebuilt the shattered authority of the crown, breaking the noble leagues, reforming justice through the Ordenamiento de Alcalá, and reasserting royal control over towns and revenues. With the kingdom in hand, he turned to the Reconquista frontier, where a new danger had arisen: the Marinid sultans of Morocco, invited by Granada, threatened a great counter-invasion.
In October 1340 Alfonso, allied with Portugal, met the combined Marinid and Granadan army at the River Salado near Tarifa and destroyed it — the last great Muslim invasion of the Iberian Peninsula, and a victory that echoed across Christendom. He followed it up with the long and successful siege of Algeciras (1342–1344), a key Muslim port.
In 1350 Alfonso XI was besieging Gibraltar, the last Muslim stronghold on the strait, when the Black Death swept through his army. The king caught the plague and died before the walls on 26 March 1350 — the only reigning European monarch to die of the great pandemic. He was succeeded by his legitimate son, Peter, later called the Cruel.
Alfonso XI is remembered as one of the strongest of medieval Castilian kings — the ruler who tamed the anarchy of his minority, restored the power of the crown, reformed its law, and won at Río Salado one of the decisive victories of the Reconquista. But his legacy was double-edged: his devotion to Leonor de Guzmán and their sons set his legitimate heir Peter against the illegitimate Trastámara line, igniting the Castilian civil war that would consume his son's reign and change the dynasty.