A major Iberian kingdom that expanded through warfare, dynastic politics, and union with Aragon.
Castile grew from a fortified frontier county of León — its name from the castles studding the upper Ebro marches — into the largest and most aggressive of the Iberian Christian kingdoms: royal from 1065, permanently united with León from 1230, master of Toledo, Seville, and Córdoba, and the crown whose late medieval union with Aragon created Spain.
Its medieval arc runs from the semi-legendary judge-counts and Fernán González's hereditary county, through the Cid's century and the great thirteenth-century conquests of Fernando III, to the legalist empire-building of Alfonso X's Siete Partidas, the civil war of Peter the Cruel and the Trastámara usurpation of 1369, and the marriage of Isabella of Castile to Ferdinand of Aragon in 1469 that pointed past the Middle Ages.
Castile began in the ninth century as León's eastern shield: a land of refugee-settlers, free peasant-warriors, and counts commanding the castle line against Córdoba's raiding armies. Count Fernán González (d. 970) made the command hereditary and practically autonomous, and Castilian custom — law spoken by local judges rather than the Gothic code of León — became a badge of the difference.
Kingship came by inheritance politics: Sancho III the Great of Navarre absorbed Castile by marriage, and at his death in 1035 left it to his son Fernando I as a kingdom in embryo; Fernando promptly took León too, and the title "king of Castile" entered permanent use with the partitions among his sons after 1065. From Alfonso VI's conquest of Toledo in 1085, Castile's centre of gravity — and its claim to lead the Reconquista — sat on the Tagus.
The century after Toledo was frontier war at its most fluid: Almoravid counter-crusade destroying Alfonso VI's armies at Sagrajas (1086) and Uclés (1108); the freelance epic of Rodrigo Díaz — El Cid — holding Valencia (1094–1102); the dynastic chaos of Urraca's reign; and the long duel of Alfonso VIII with both Almohads and Christian neighbours, from the disaster of Alarcos in 1195 to the redeeming triumph of Las Navas de Tolosa in 1212, won with Aragon and Navarre under a crusading bull.
Fernando III (1217–1252) reunited Castile and León in 1230 and broke Almohad Iberia: Córdoba fell in 1236, Jaén in 1246, Seville after a two-year siege in 1248, leaving only vassal Granada. His son Alfonso X "the Wise" (1252–1284) converted conquest into culture and law — the Siete Partidas, the vernacular chancery, the school of translators at Toledo, the imperial candidacy that drained his treasury — while the mudéjar revolts and noble leagues he provoked set the pattern of late medieval Castilian turbulence.
The fourteenth century brought the strait's last African war — Alfonso XI's great victory at the Salado in 1340 with Portuguese help, and his death of plague besieging Gibraltar in 1350 — then dynastic catastrophe: the civil war of Peter the Cruel and his bastard half-brother Henry of Trastámara, fought with English and French armies inside the Hundred Years' War (the Black Prince winning Nájera for Peter in 1367, Bertrand du Guesclin's companies winning Montiel and the regicide for Henry in 1369).
Trastámara Castile was a great power run by a quarrelsome high nobility: Henry II's "mercedes" bought loyalty with alienated royal lands; John I lost Aljubarrota and with it the Portuguese crown in 1385; the long minorities of Henry III and John II handed government to regents and favourites — Álvaro de Luna above all, master of Castile for thirty years until his execution in 1453. Through it all the machinery matured: cortes of the three estates, the audiencia as high court, the hermandades policing the roads, and the wool of the Mesta funding crown and fleet.
Castilian kingship was hereditary, sacral in style, and — by the Partidas' Roman-law doctrine — theoretically absolute: the king as emperor in his kingdom, source of law and justice. Practice was bargained: the cortes of Castile and León (townsmen present from the twelfth century) voted the servicios taxation and heard grievances; the great magnate houses (Lara and Haro early; Mendoza, Guzmán, Velasco later) and the masters of Santiago, Calatrava, and Alcántara commanded private armies the crown alternately used and fought.
The kingdom's administrative signature was the town: hundreds of fuero-chartered concejos with vast frontier territories, urban knight-militias (caballeros villanos) owing cavalry service, and — from Alfonso XI's reform of 1348 — royal regidores steering their councils. Royal justice travelled through adelantados and corregidores; the Partidas, given binding force in 1348, made Castile the peninsula's great Roman-law monarchy.
Fernán González, count c. 931–970 — made Castile hereditary and effectively autonomous within León.
Alfonso VI of Castile and León, 1065/1072–1109 — conqueror of Toledo (1085); the Cid's difficult sovereign.
Alfonso VIII of Castile, 1158–1214 — survivor of Alarcos and victor of Las Navas de Tolosa (1212).
Fernando III, 1217–1252 — union with León (1230) and the conquests of Córdoba, Jaén, and Seville; canonised in 1671.
Alfonso X the Wise, 1252–1284 — the Siete Partidas, the Toledo translators, the imperial dream and its debts.
Alfonso XI of Castile, 1312–1350 — victor of the Salado (1340), reformer of town government, dead of plague before Gibraltar.
Peter of Castile, 1350–1369 — "the Cruel" to his enemies; his war with the Trastámaras merged into the Hundred Years' War and ended at Montiel.
Henry II of Castile, 1369–1379 — the usurper-founder of the Trastámara dynasty.
John I of Castile, 1379–1390 — pressed the Portuguese claim to defeat at Aljubarrota (1385).
John II of Castile, 1406–1454 — the long reign of favourites, Álvaro de Luna's Castile, and the eve of the Catholic Monarchs.