Sixtus IV (sĭkˈstəs) [key], 1414–84, pope (1471–84), an Italian named Francesco della Rovere (b. near Savona); successor of Paul II. He was made general of his order, the Franciscans, in 1464 and became (1467) a cardinal. Sixtus was expected to be a reformer, but he was too much embroiled in political difficulties. The struggle with the French monarchy over the control of the church in France was complicated by Louis XI's efforts to replace Ferdinand I of Naples with a Frenchman. A quarrel with Lorenzo de' Medici became critical after the Pazzi conspiracy (1478), since an important instigator was Girolamo Riario, nephew of Sixtus, and the pope seems to have had prior knowledge of the plot. He waged war on Florence afterward. Though a reconciliation was made in 1479, Lorenzo joined Louis XI in threatening schism. Relations with Italian states other than Florence were also unhappy. Sixtus consented (1478) to the establishment of the Spanish Inquisition and then found the Spanish ignoring his rebukes for illegal procedure and jurisdiction and his demands for moderation. He welcomed into the Papal States the Jews expelled from Spain. The behavior of his favored nephews was disgraceful; a happy exception was Giuliano della Rovere (later Pope Julius II). Sixtus was an excellent administrator of the city and did much to improve and beautify Rome. He was an important benefactor of the Vatican Library, and he founded the Sistine Chapel. He summoned Josquin Desprez to Rome and legislated for the improvement of church music. He was succeeded by Innocent VIII.
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