Isabella I or Isabella the Catholic, 1451–1504, Spanish queen of Castile and León (1474–1504), daughter of John II of Castile. In 1469 she married Ferdinand of Aragón (later King Ferdinand II of Aragón and Ferdinand V of Castile). At the death (1474) of her half-brother Henry IV of Castile, the succession to Castile was contested between Isabella and Juana la Beltraneja, who was supported by Alfonso V of Portugal. The civil war ended with Isabella's victory in 1479, the year in which Ferdinand became king of Aragón. Isabella and Ferdinand, known as the Catholic kings, ruled Castile and Aragón jointly. Although the union of their crowns was personal rather than institutional, their reign in effect marked the beginning of the unified Spanish kingdom. Isabella's principal aim was to assert royal authority over the lawless Castilian nobility. To this end she revived the medieval hermandad and confiscated the lands of many magnates. She also took over the administration of the holdings of the powerful religious military orders (by making Ferdinand their grand master) and established the Inquisition under royal control. She was a prime mover in the expulsion (1492) of the Jews from Spain, the conquest (1492) of Granada, and the forced conversion of the Moors. She showed foresight in her patronage of Christopher Columbus. The Catholic kings furthered learning and the arts and promoted great building activity. The style of the period is called isabelino after the queen; it combines Gothic, Mudejar, and Renaissance features. Isabella bequeathed Castile to her daughter Joanna, with Ferdinand as regent.
See biographies by I. L. Plunket (1915), W. T. Walsh (1987), and K. Downey (2014); W. H. Prescott, History of the Reign of Ferdinand and Isabella the Catholic (3 vol., 1838; abr. ed. 1962); J. H. Mariéjol, The Spain of Ferdinand and Isabella (1892, tr. 1961); R. B. Merriman, The Rise of the Spanish Empire, Vol. II (1918, repr. 1962); J. H. Elliott, Imperial Spain: 1469–1716 (1963).