Sixtus IV

Francesco della Rovere came to the papacy from the Franciscan order, where he had been minister general and a working theologian who wrote on the blood of Christ and on the Immaculate Conception. What he is remembered for is not the theology but the building. Between 1473 and 1481 he had the old papal chapel in the Vatican rebuilt to proportions that later scholars noticed match those given for the Temple of Solomon in the book of Kings, and had its walls frescoed by Perugino, Botticelli, Ghirlandaio and Cosimo Rosselli with paired scenes from the lives of Moses and Christ. It has been called the Sistine Chapel after him ever since, and it is where his successors have been elected for five centuries.

He also gave the Vatican Library its institutional life. A papal collection had existed before him, but in 1475 he formally established it with an endowment, rooms and a staff, and appointed the humanist Bartolomeo Platina as its first librarian, a moment Melozzo da Forli painted with the pope enthroned among his nephews. Under Sixtus the collection roughly doubled and became a scholarly resource rather than a private hoard. He rebuilt streets and bridges across Rome, including the Ponte Sisto, in preparation for the jubilee of 1475.

The cost of all this was met partly by an aggressive extension of family power. Six of his nephews were made cardinals, one of them Giuliano della Rovere, who would rule as Julius II and finish much of what his uncle began. Contemporaries objected loudly, and the Florentine crisis of 1478, in which the Pazzi conspirators killed Giuliano de Medici during Mass in the cathedral, drew Sixtus into a war with Florence and left a stain his defenders have argued over ever since.

In November 1478, at the request of Ferdinand of Aragon and Isabella of Castile, Sixtus IV issued the bull Exigit sinceras devotionis affectus, permitting the Spanish crown to appoint inquisitors in its own territories. Inquisition tribunals had existed in the medieval church for two and a half centuries, but this one was different in a way that mattered: the crown, not the papacy, named and controlled the inquisitors. Within four years reports of its severity against conversos, Jews who had accepted baptism, reached Rome, and in April 1482 Sixtus issued a brief protesting that the tribunal was proceeding on the testimony of enemies and slaves and imprisoning the innocent. Ferdinand refused to accept the correction, and the pope, needing Spanish support elsewhere, did not press it. The institution he authorized outlived him by three and a half centuries.

The second decision was doctrinal in form and financial in effect. The bull Salvator Noster of 1476 extended the benefit of an indulgence to souls already in purgatory, obtainable by the living on their behalf. The reasoning drew on a developed theology of the communion of saints, but the practical result was a new and highly saleable category of pious giving, and it is a direct ancestor of the preaching that provoked Martin Luther in 1517.

Against these stands a decision of a different temper. The Immaculate Conception of Mary was fiercely disputed between Franciscans and Dominicans in his day. Sixtus approved a feast and office for it in 1476 and then, in 1483, forbade either party to accuse the other of heresy for the position it held, leaving the question open for another three and a half centuries.