Sixtus founded the Spanish Inquisition through the bull Exigit sincerae devotionis affectus (1478), and he annulled the decrees of the Council of Constance.

[3] As a young man, Della Rovere joined the Franciscan Order, an unlikely choice for a political career, and his intellectual qualities were revealed while he was studying philosophy and theology at the University of Pavia.

Before his papal election, Cardinal della Rovere was renowned for his unworldliness and had written learned treatises, including On the Blood of Christ and On the Power of God.

[5] His reputation for piety was one of the deciding factors that prompted the College of Cardinals to elect him Pope upon the unexpected death of Paul II at the age of fifty-four.

[10] Chroniclers of his life seem to regard his death as unnatural and thus connect his alleged grandiose spending habits and the impression they left on his contemporaries as causal.

According to the later published chronicle of the Italian historian Stefano Infessura, Diary of the City of Rome, Sixtus was a "lover of boys and a sodomite" (Latin: puerorum amator et sodomita) awarding benefices and bishoprics in return for sexual favours and nominating a number of young men as cardinals.

[18] The English churchman and Protestant polemicist John Bale, writing a century later, attributed to Sixtus "the authorisation to practice sodomy during periods of warm weather" to the "Cardinal of Santa Lucia".

[4] That was a cornerstone of the privileges claimed for the Gallican Church and could never be shifted as long as Louis XI manoeuvred to replace King Ferdinand I of Naples with a French prince.

On 1 November 1478, Sixtus published the papal bull Exigit Sincerae Devotionis Affectus through which the Spanish Inquisition was established in the Kingdom of Castile.

[22] As a temporal prince who constructed stout fortresses in the Papal States, he encouraged the Venetians to attack Ferrara, which he wished to obtain for another nephew.

[4] For refusing to desist from the very hostilities that he himself had instigated and for being a dangerous rival to Della Rovere dynastic ambitions in the Marche, Sixtus placed Venice under interdict in 1483.

[23] The two papal bulls issued by Pope Nicholas V, Dum Diversas of 1452 and Romanus Pontifex of 1455, had effectively given the Portuguese the rights to acquire non-Christian slaves along the African Coast by force or trade.

That was part of a broader scheme of urbanization carried out under Sixtus IV, who swept the long-established markets from the Campidoglio in 1477 and decreed in a bull of 1480 the widening of streets and the first post-Roman paving, the removal of porticoes and other post-classical impediments to free public passage.

[8] He had Regiomontanus attempt the first sanctioned reorganisation of the Julian calendar[28] and increased the size and prestige of the papal chapel choir, bringing singers and some prominent composers (Gaspar van Weerbeke, Marbrianus de Orto and Bertrandus Vaqueras) to Rome from the north.

[29][30] As Pope, he issued a papal bull allowing local bishops to give the bodies of executed criminals and unidentified corpses to physicians and artists for dissection.

It was that access to corpses which allowed the anatomist Vesalius, along with Titian's pupil Jan Stephen van Calcar, to complete the revolutionary medical/anatomical text De humani corporis fabrica.

[citation needed] The Pope created 34 cardinals in eight consistories held during his reign, among them three nephews, one grandnephew and one other relative, thus continuing the practice of nepotism that he and his successors would engage in during this period.

His bronze funerary monument, now in the basement Treasury of St. Peter's Basilica, made like a giant casket of goldsmith's work, is by Antonio del Pollaiuolo; it was completed by 1493.

The overall program of the panels, their beauty, complex symbolism, classical references and their relative arrangement are compelling and comprehensive illustrations of the Renaissance worldview.