Pope Sixtus IV (1414-1484)

Popular memory often retains only one thing about Sixtus IV: the chapel that bears his name and that another, Michelangelo, would make immortal half a century later. The reality of the man is denser and more uncomfortable.

Sixtus IV was not a worldly pope by formation: he was a Franciscan friar, entered the order as a child, became one of the most respected theologians of his time, Minister General of his Order before becoming cardinal. When he ascended the throne of Peter in 1471, the Church expected from him a crusade against the Turks and reform. Thirteen years later, he left behind an enhanced Rome, a revived library, a strengthened Marian devotion — but also a papacy deeply involved in the politics of the Italian principalities, where the pope acted less as a universal shepherd than as a territorial lord concerned with establishing his nephews.^[11][12]

This is precisely what makes his pontificate instructive. It illustrates the tension of the Renaissance papacy: a Roman See regaining its cultural brilliance and defending the faith doctrinally, while being drawn into the dynastic and military logic of its time. Neither hagiography nor black legend: Sixtus IV demands a perspective that distinguishes what serves the Church from what harms it, and recognizes that the holiness of the institution does not depend on the personal holiness of each pontiff.

An Obscure Ligurian Birth (1414)

Francesco della Rovere was born on July 21, 1414, in the region of Savona, Liguria. Sources differ on the exact village: tradition holds Celle Ligure, while the Catholic Encyclopedia states he was born near Albisola.^[13][14] Both locations are neighboring towns on the Ligurian coast, and the debate is minor. What matters most is that he came from a poor family, unrelated to the great aristocracy that then dominated the conclaves.^[15]

This modest origin made him, like Adrian IV three centuries earlier, a man whose rise to the highest ranks was due solely to ecclesiastical merit. As a child, he was destined for the Order of Friars Minor—likely by a vow of his parents during an illness, according to a tradition reported by his biographers. It was the Franciscan cloister, not family wealth, that shaped him.

The Theologian: Pavia, Padua, Bologna

The young friar showed remarkable intelligence. He studied philosophy and theology at the University of Pavia, then taught successively at Padua, Bologna, Pavia, Siena, and Florence.^[16] His reputation as a master was such that the Greek cardinal Bessarion, one of the highest intellectual figures of the 15th century, counted among his interlocutors and admirers.^[17]

He was therefore not a courtier who had arrived by chance, but a recognized academic, skilled in scholastic disputation. This formation explains two traits of his pontificate: his passion for books—which led him to refound the Vatican Library—and his taste for precise theological controversy, notably on the Immaculate Conception, where he sought to reconcile Thomists and Scotists.

Minister General of the Order of Friars Minor (1464)

After serving as procurator of his Order in Rome and then provincial of Liguria, Francesco della Rovere was elected Minister General of the Franciscans in 1464, at the age of fifty.^[18] This was the highest office in one of Christendom’s largest orders, with thousands of convents across Europe.

Governing the Friars Minor meant managing a vast institution, marked by tensions between the Conventuals and the Observants. This experience as a large-scale administrator directly prepared the future pope: when he would have to organize a Jubilee, finance building projects, or reorganize the Curia, he would not be starting from scratch.

Cardinal of Saint Peter in Chains (1467)

In 1467, Pope Paul II made him a cardinal, assigning him the titular church of San Pietro in Vincoli (Saint Peter in Chains).^[19][20] The Franciscan thus entered the Sacred College. Four years later, at Paul II’s death, the conclave turned to this renowned theologian, without great wealth or a powerful Roman clientele—a profile that, on paper, promised a reforming pontificate.

Before being a builder, Sixtus IV was a theological author. This is the most forgotten aspect of his history, yet it is the one by which his name remains linked to a major doctrinal development.

De sanguine Christi and the Work on the Immaculate Conception

As early as 1470, while still a cardinal, he published a treatise on the Precious Blood of Christ (De sanguine Christi) and a work on the Immaculate Conception of the Virgin.^[21] These are the only two theological writings that the Catholic Encyclopedia attributes to him with certainty.

De sanguine Christi engages with a lively 15th-century theological controversy: did the blood shed by Christ during the Passion remain united to the divinity during the three days in the tomb? Sixtus, as a Franciscan theologian, rigorously took part in the debate. These works reveal a man who thought faith from within, not merely a patron of letters.

Defender of the Immaculate Conception

Sixtus IV’s major doctrinal contribution concerns the Immaculate Conception—the truth, not yet defined as dogma, that the Virgin Mary was preserved from original sin from the very first moment of her conception. In the 15th century, this question sharply divided the Franciscans, defenders of this preservation following Duns Scotus, and some Dominicans, more reserved in the line of Saint Thomas Aquinas.^[22]

In his 1470 work, the future pope already sought to show that Thomas and Scotus, though differing in words, agreed in substance.^[23] Once pope, he acted. In 1476, by the apostolic constitution Cum praeexcelsa (February 28, 1476), he approved the feast of the Immaculate Conception, assigned it its own Mass and Office, and attached indulgences to it.^[24]

As the controversy continued to inflame the two schools, Sixtus IV intervened a second time. By the bull Grave nimis of September 4, 1483, he forbade the two camps from calling each other heretics:

In substance (paraphrase from the Latin, the exact French verbatim having proved impossible to verify), the bull declares false, erroneous and far from the truth the claim that those who believe or affirm that the glorious Virgin Mary was preserved from the stain of original sin sin gravely, or mortally.^[25]

This act was not a dogmatic definition—the Church had not yet decided—but a doctrinal pacification of great wisdom: it protected the freedom of Marian devotion without imposing a conclusion that the Magisterium would solemnly proclaim only in 1854, with Pope Pius IX’s bull Ineffabilis Deus.^[26] On this ground, the Franciscan Sixtus IV truly prepared the way for the dogma.

Upon the death of Paul II, the conclave held in August 1471 elected Cardinal della Rovere. He took the name Sixtus IV — a name not used since the 5th century, since Pope Saint Sixtus III.^[27] The choice of a Franciscan theologian known for his austerity raised hopes for a pontificate focused on reform and a crusade against the advancing Ottomans, just two years after the fall of Venetian Euboea.

But very quickly, the pontificate shifted toward a different logic. Sixtus IV revealed himself as a lavish patron and a territorial statesman determined to consolidate the Papal States and provide for his family. The theologian did not disappear, but was gradually overshadowed by the prince. This transformation — from a reform-minded cardinal to a dynastic pope — constitutes the inner drama of his reign.

If there is one thing that enduringly redeems the memory of Sixtus IV, it is his work as a builder and protector of letters. He transformed Rome and founded institutions that still shine today.

The Sistine Chapel (1473–1481)

The pope commissioned the construction of the great papal chapel at the Vatican, between 1473 and 1481, which would bear his name as the Sistine Chapel (Cappella Sistina).^[28] The architectural project is attributed to Baccio Pontelli, with construction overseen by Giovannino de' Dolci. The building, austere on the outside, was designed for major pontifical ceremonies and conclaves.

Between 1481 and 1482, Sixtus IV summoned the greatest Renaissance painters to adorn the side walls with frescoes depicting the Life of Moses and the Life of Christ: Perugino, Sandro Botticelli, Domenico Ghirlandaio, and Cosimo Rosselli.^[29] The chapel was consecrated on August 15, 1483, the Feast of the Assumption, and dedicated to the Virgin Mary — perfectly consistent with the pope’s Marian devotion.^[30] The famous ceiling by Michelangelo would come only under his nephew Julius II, nearly thirty years later; but without Sixtus IV, this masterpiece would have had no vault to cover.

The Vatican Library: The Second Founder

A humanist passionate about books, Sixtus IV gave the Apostolic Vatican Library its first lasting organization. By the bull Ad decorem militantis Ecclesiae of June 15, 1475, he endowed the library with premises, regular income, and staff, and officially appointed the humanist Bartolomeo Platina as librarian (gubernator et custos).^[31] For this reason, he is considered the second founder of the Vatican Library.^[32]

This scene was immortalized by the painter Melozzo da Forlì in a famous fresco showing the pope, surrounded by his nephews, instituting Platina kneeling before him. The bull, in its preamble, justifies the effort by the very dignity of the Church:

In substance (a paraphrase of the Latin, since the exact French wording could not be checked against the official text), the preamble assigns a threefold purpose to the foundation: the adornment of the militant Church, the increase of the Catholic faith, and the convenience of scholars devoted to study.^[33]

The Ponte Sisto, the Jubilee of 1475, and the Renovation of Rome

In preparation for the Jubilee of 1475, which was expected to draw crowds of pilgrims, Sixtus IV undertook extensive works. He rebuilt a bridge over the Tiber, the Ponte Sisto (completed around 1473–1479), to ease traffic between the two banks and prevent a new tragedy like that of 1450, when about two hundred pilgrims were crushed on the old Ponte Sant’Angelo.^[34][35] He widened and paved streets, restored many churches, rebuilt the Hospital of the Holy Spirit (Santo Spirito in Sassia), and commissioned the church of Santa Maria del Popolo.^[36][37]

Under his pontificate, Rome ceased to be the half-ruined city of the Avignon return and became once again a capital worthy of Christendom. This was one of the foundations of the Renaissance Rome that his successors would continue.

The Capitoline Bronzes: The First Public Museum (1471)

In the very first year of his pontificate, in 1471, Sixtus IV made a gesture of immense cultural significance: he gave the Roman people a series of ancient bronzes previously kept at the Lateran — the Capitoline Wolf, the Spinario (Boy with Thorn), the Camillus, and the colossal head of Emperor Constantine with his hand and globe.^[38]

This donation, made to the people and not to a prince, founded what is considered the first public museum in history, the nucleus of the future Capitoline Museums.^[39] The Franciscan theologian, by restoring to the Romans the symbols of their past, unknowingly inaugurated the modern idea of common heritage.

Behind these glories, one flaw dominates and corrupts everything else: nepotism, that is, the use of papal power to enrich and elevate one’s own relatives. The Catholic Encyclopedia states it bluntly: it was his worst vice.^[40]

The Cardinal Nephews

Sixtus IV created six of his nephews or relatives as cardinals, some very young and without real ecclesiastical merit.^[41][42][43] The following table summarizes these six cardinali nipoti and their fates:

Girolamo Riario, for his part, remained a layman — lord of Imola and Forlì, at the heart of the military intrigues, assassinated in 1488 — and was never a cardinal.

This massive promotion of relatives is not a mere moral detail: it shaped the Holy See’s foreign policy. The Italian wars waged by Sixtus IV are largely explained by his desire to carve out principalities for his lay nephews, foremost among them Girolamo Riario.^[44]

A Paradigmatic Example That Fixed the Word “Nepotism”

The phenomenon was so blatant under Sixtus IV and his immediate successors that the language preserved the trace. The word “nepotism” comes from the Italian nipote, meaning “nephew”: it specifically denotes the Renaissance popes’ practice of elevating their nephews to the highest offices.^[45] Sixtus IV did not invent the abuse, but he became one of its paradigmatic examples, paving the way for the excesses that would culminate with the Borgia popes.

Nepotism drew Sixtus IV into the bloody politics of the Italian principalities, where he acted as head of state as much as shepherd.

The Pazzi Conspiracy (1478)

The darkest episode was the Pazzi conspiracy on April 26, 1478, in Florence. The Pazzi family, rivals of the Medici, plotted to overthrow Lorenzo the Magnificent and his brother Giuliano de’ Medici. The attack took place during Mass in Florence Cathedral: Giuliano was stabbed to death, but Lorenzo, wounded, survived.^[46][47]

The pope’s role in this affair remains debated, but it is established that Sixtus IV had approved the plan to overthrow the Medici, who were seen as hostile to his policies and to his nephew Girolamo Riario. Tradition holds that he demanded the operation be carried out “without bloodshed” — a diplomatic phrase that did not prevent the massacre.^[48] His nephew, Cardinal Raffaele Riario, was present in the cathedral at the time of the attack. Following the assassination, the conspirator archbishop Francesco Salviati was hanged from the windows of the Palazzo della Signoria, provoking the pope’s fury and war.

The War Against Florence

In retaliation for the execution of implicated clerics, Sixtus IV excommunicated Lorenzo de’ Medici, placed Florence under interdict, and went to war against the city (1478-1480), allied with Naples.^[49] This conflict, largely motivated by political and familial reasons, shows the Renaissance papacy as an active participant in Italian rivalries, disregarding its role as spiritual arbiter. Peace returned only after two years, when the Turkish threat to Otranto (1480) forced Christian princes to reconcile.

The War of Ferrara (1482-1484)

A few years later, Sixtus IV encouraged Venice to attack Ferrara (1482), again to serve the territorial ambitions of Girolamo Riario.^[50] When the coalition turned against its own interests, the pope switched sides and eventually imposed the interdict on Venice that he had initially supported. The Peace of Bagnolo (August 7, 1484), concluded without him, caused according to Pastor — who here follows the contemporary Sigismondo de' Conti — extreme grief that aggravated his illness. He died five days later, on August 12, 1484.^[51]

One last controversial act marked his pontificate. At the request of sovereigns Ferdinand of Aragon and Isabella of Castile, Sixtus IV signed the bull Exigit sinceras devotionis affectus on November 1, 1478, which authorized the establishment of the Inquisition in Spain under the authority of the Crown.^[52]

It is essential to distinguish this Spanish Inquisition — largely controlled by the state, whose abuses worried Rome — from the medieval papal inquisition. As early as 1482, alarmed by reports of unjust procedures and confiscations, Sixtus IV tried to curb excesses and remind authorities of the rights of the accused, issuing a brief denouncing abusive imprisonments.^[53] But the pressure from the Spanish Crown was too strong, and the pope failed to regain control of an apparatus that increasingly slipped from the Church’s grasp. For the black legend that arose from this, see the dossier The Inquisition and Its Black Legend.

Despite his Italian entanglements, Sixtus IV did not forget the Ottoman threat. After the recent fall of Constantinople (1453), he financed a papal fleet and sent legates to preach the crusade.^[54] The results were meager: the crusade achieved almost nothing, due to the lack of lasting unity among Christian princes.^[55] The recapture of Otranto from the Turks in 1481, following their landing in 1480, was the only notable success of this policy.

The pope also attempted to bring the Church of Rome and the Russian Church closer together, following the line of the Council of Florence (1439), but without lasting success.^[56] These efforts, even if unsuccessful, remind us that beneath the territorial prince remained a consciousness of a universal responsibility for Christendom.

The Lights

To Sixtus IV’s credit, history records first-rate achievements. The Sistine Chapel and the Vatican Library remain to this day living centers of the Church and global culture. The renovation of Rome, the Ponte Sisto, and the Capitoline bronzes refounded the city. Doctrinally, his defense of the Immaculate Conception and his wise pacification between Franciscans and Dominicans prepared a dogma that the Church would proclaim four centuries later. The theologian of the Precious Blood never ceased to inhabit the prince.

The Shadows

On the debit side, nepotism dominates, along with the Italian wars, the Pazzi conspiracy, and the signing of the bull opening the way to the Spanish Inquisition. These faults are not mere blunders: they reveal a papacy which, in the Renaissance, too often confused the interests of the Church with those of a family. Sixtus IV thus opened the slope that would lead, twenty years later, to the decline of the Borgia popes.

Why Sixtus IV Matters Today

The lesson of Sixtus IV is that of the Catholic distinction between the man and the office. The Church has never taught that its pontiffs would be personally holy; it teaches that the indefectibility of the See of Peter does not depend on their private virtues. A pope can build chapels, refound libraries, defend a Marian truth—and yet commit grave faults through dynastic ambition. The Catholic Encyclopedia expresses this with rare balance:

“Nevertheless, there is a praiseworthy side to his pontificate... his worst vice was nepotism, and his greatest misfortune was that he was destined to be placed at the head of the States of the Church at a time when Italy was emerging from the era of the republics.” — The Catholic Encyclopedia, art. “Pope Sixtus IV”^[57]

To understand Sixtus IV is therefore to learn to give thanks for the works without excusing the faults, and to see in the history of the papacy not a gallery of spotless saints, but a continuity that neither vices nor compromises have ever broken.

• The Dogma of the Immaculate Conception, whose feast Sixtus IV approved (Cum praeexcelsa, 1476) and whose controversy he pacified (Grave nimis, 1483)
• The Decline of the Borgia Popes, the culmination of the nepotistic drift of which Sixtus IV was a forerunner
• The Christian Renaissance, of which Sixtus IV was one of the great pontifical patrons
• The Construction of the Current St. Peter’s Basilica, launched by his nephew Julius II, who commissioned Michelangelo to paint the Sistine Chapel ceiling
• The Inquisition and Its Black Legend, to place the 1478 bull in its real context