St. Leo the Great vs. Manichaean Pedophiles

By Thomas V. Mirus ( bio - articles - email ) | Aug 18, 2026 | In Lives of the Popes

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45—St. Leo I (440-461)

We have now arrived at the first of only three popes whom history has remembered as “the Great.” Leo is so important, and we know so much more about him than about previous popes, that I will be covering his reign over several installments.

The bishop of Rome has, and had at St. Leo’s time, multiple layers of primacy. First, of course, is his role as the pastor of the church in Rome itself. More than that, he is the metropolitan of the Roman Province including other dioceses in southern Italy. More than that, he is Patriarch of the West. And finally, because of the smallest of those spheres of authority—his being bishop of the city of Rome—he is also the Supreme Pontiff of the Universal Church, including the East. My narrative of Leo’s reign will be organized according to these progressively larger spheres of jurisdiction, and as you might expect, the story gets more consequential and dramatic as it increases in scale.

Why is Leo called “the Great”? We will see his greatness clearly enough in the details of his reign, but for introductory purposes, here are the broad strokes:

First, there is his influence on the papacy itself. Leo’s modern reputation as the “creator of the papacy” or of the “medieval papacy” is a false one, as this series has shown his predecessors consciously wielding their authority over the Church—but still, the Church’s full teaching on papal primacy and infallibility is especially clearly present in the writings of Pope Leo, in which he educes the Scriptural basis of his office. His rule enhanced the practical moral and legal authority of the bishop of Rome, making him a greatly important figure in the development of the papacy.

St. Leo was exacting in his enforcement of Christian morals, doctrine, and canon law, yet always merciful, eager to offer a second chance. He never stopped hoping for the conversion of heretics even after they had been condemned.

Leo governed the churches around the world energetically yet with prudence and tact, patient in waiting until he had sufficient and reliable information before making a decision. He intervened when necessary, but often precisely to defend the traditional and legal rights of local bishops.

He consistently stood up for the integrity of the Church’s doctrine and discipline against imperial meddling, but again, with great tact. He knew what to stand firm on, but also when to pass over an issue he cared about for the sake of even more important matters. But while maintaining the spiritual independence of the Church from the state, he was often able to put the state to work for the Church, even against the initial preferences of emperors who had their own agendas.

Pope Leo treated the legal decisions of his predecessors as having equal weight to the canons of councils, contributing to the formation of canon law.

Leo wrote one of the great formulations of Christian orthodoxy, the so-called Tome of Leo, expressing the correct understanding of the two natures of Christ. Through this letter, he was the decisive voice at one of the Church’s most doctrinally important ecumenical councils, the Council of Chalcedon.

And of course, St. Leo the Great is famous for being the pope who convinced Attila the Hun to turn around and go back the way he came.

Leo was likely born of Etruscan descent in the Tuscan city of Volterra. It seems that his family at some point migrated to Rome, perhaps because of the Gothic incursions into northern Italy.

Early in his ecclesiastical career, Leo was likely a bearer of letters from Pope St. Zosimus to other bishops. At some point during the pontificate of St. Celestine I, he was ordained a deacon; indeed he was archdeacon under Popes Celestine and Sixtus III. The archdeacon was, under the Pope, the most influential figure in the Roman Church. For instance, it was Leo who prevailed upon St. John Cassian to weigh in on the Nestorian controversy during the lead-up to the Council of Ephesus. He was also the likely compiler of a collection of papal and conciliar documents related to the Pelagian controversy.

When St. Sixtus III died, all of Rome knew whom they wanted to succeed him. A delegation was sent to retrieve Leo from a political mission he was engaged in, and on his return he was unanimously elected bishop of Rome. He was consecrated on September 29, 440, and the first of his collected sermons is the one he gave on that occasion. He would likewise preach on the anniversary of his consecration for the first several years of his papacy.

In that first sermon, Leo embraced his new office with joyful confidence in his divine mission—with real humility, indeed, but not with any self-deprecating protestation of not being up to the task:

“Let my mouth speak the praise of the Lord, and my soul and spirit, flesh and tongue, bless his holy Name.” Failure to acknowledge benefits conferred by God is a mark rather of ingratitude than of modesty, and what is more fitting than that the ministry of a (newly) consecrated bishop should begin with the sacrifice of praise to the Lord? …I therefore will give thanks to our God, and will ever so do “for all the benefits that He hath done unto me.” Besides this, I join with you in celebrating with fitting gratitude your favorable choice, for I, as one who with the care of a shepherd longs for the salvation of your souls, recognize how much respect, love and confidence your devoted affection has shown to myself, when in spite of my lack of merits in the past you have given your verdict so generously in my favor. So I beg of you, by the mercy of God, aid with your prayers him whom you have sought to the fulfilment of your wishes, so that the grace of God may abide in me and that your confidence in myself may not waver.

Leo would serve the Church as Pope for the next twenty-one years.

Quashing the Manichaeans in Rome

St. Leo lived in a time of recurring barbarian invasions. When he was elected, it had only been thirty years since Alaric’s siege of Rome in 408 and his sack of the city in 410. The population of the city was between one and two million.

To get a sense of how Catholics in Rome would have related to Pope Leo, it is worth noting that there were no parish priests in Rome until the end of the fifth century. There were parish churches, but the priests were sent around as needed rather than having a consistent parish assignment. So a Catholic in Rome would likely have felt the bishop, not a parish priest, to be his true pastor.

Much of our information about Leo’s reign comes from his surviving letters, which were generally written to fellow bishops or to some imperial personage.

Of what we know of Leo’s rule over his own diocese, most important is his response to the Manichaean threat. As is well known because of St. Augustine’s Confessions, Manichaeism was much more established in Africa. But there was also an increasing presence of Manichaeans in Italy and in Rome itself, partly because they were among the refugees fleeing the Vandal conquest of north Africa.

Having heard about the immoral nature of the Manichaean rites, Leo launched an investigation in collaboration with the civil authorities, which he would describe in a sermon shortly afterward. A court was held in which various Manichaeans were questioned, including a “bishop.” Among other things, it came to light that a recent ritual had included the ceremonial deflowering of a ten-year-old girl. This was established beyond doubt by the testimony of the very people responsible for the act.

The result of the investigation as a whole was that those Manichaeans who were willing to repudiate the teaching of their cult were lightly punished, while those who held onto their doctrines were banished for life. This was, in fact, an enforcement of anti-Manichaean legislation that had been adopted by the Roman state a century and a half earlier.

That was the beginning of Leo’s battle against the Manichaeans, and it is not surprising that their abhorrent rites, alongside their erroneous doctrines, motivated him to preach against them so frequently. In particular, he would repeatedly warn against their denial of the Christian doctrine of the Incarnation.

He even told his flock that if they knew of any Manichaeans in their community, they should give their names to a priest in order to assist in the defeat of this sect. Denouncing a Manichaean was an act meritorious before God. This could be easier or harder depending on the sneakiness of the Manichaeans in question, since some pretended outwardly to conform to orthodox doctrine and practice.

Leo also informed the other bishops of southern Italy of what had happened in Rome, encouraging them to deal with the Manichaeans in their districts, including those who had fled the capital to escape arrest. He sent word to the Eastern churches as well to warn them of the danger of this sect. And he likely influenced an edict of the Western Emperor Valentinian a year and a half later, which penalized Manichaeans in various ways, including banning them from the civil service, from urban residence, and from either inheriting or willing property.

Biographer Trevor Jalland notes that this was “the first known example of a partnership between Church and State in carrying out a policy of religious persecution”—though I would not use the word persecution in a pejorative sense, nor would I weep over the Manichaeans’ religious liberty, especially given the sect’s danger to public morality. At any rate, Leo’s campaign against Manichaeism in Rome seems to have succeeded.

This seems to have been the main religious threat in Leo’s local church. He also warns in his sermons against monophysitism, and against customs which were a holdover from pagan superstition, but these were less of a concern.

St. Leo made restorations and improvements to the basilicas of St. Peter and St. Paul outside the walls, and placed guards to protect the relics of the two Apostles of Rome. He also founded a monastery associated with St. Peter’s. It has been said that he added the words “a holy sacrifice, a spotless victim” to the Canon of the Mass.

Sacramental discipline in the Roman Province

The local authority of the bishop of Rome extended beyond the city itself. He was also the metropolitan of the Roman Province, with a particular responsibility for the so-called “suburbicarian” churches, literally meaning “under the city.” At the time of Pope Leo, these included the churches of southern Italy, Sicily, Corsica, and Sardinia.

In the early 440s, St. Leo wrote to the bishops of Campania, Picenum, and Tuscany to address various abuses in the administration of Holy Orders. This included the consecration of bishops who had married widows or who had been married more than once, against the rule put forth in the New Testament.

Another issue was the ordination of men of low social status, which he forbade on the grounds that it degraded the priesthood due to their lack of qualifications, but also because many such people had hereditary obligations to labor, or were even slaves or serfs. Such men would be unable to devote themselves fully to priestly ministry, and besides, Leo said, this would infringe on the rights of their employers. Any such person who had already been ordained was forbidden to hold office or to be made a bishop. In this, Leo was enforcing already-established canons of the Church. He also forbade clerics and laity to practice usury.

In this letter, Leo made a point of confirming disciplinary decrees of previous popes. Trevor Jalland notes: “The importance of his action lies in the fact that it enables us to trace the beginning of the process by which papal decretals, side by side with the formal enactments of important councils, came to possess the force of canon law.”

St. Leo was also concerned about a local custom in Sicily and elsewhere of baptizing people on the feast of Epiphany. He wrote with great indignation to the Sicilians that this custom was contrary to the custom of apostolic origin, which was to baptize on Easter and Pentecost.

I am amazed that you or your predecessors should have followed such an absurd innovation, as by confusing the hidden meaning of the two seasons to suggest that no difference exists between the day on which Christ was worshipped by the Magi and the day on which Christ rose from the dead.

In this Letter 16, which is well worth reading, Leo explains that various liturgical seasons and feasts have particular mystical meanings, making the celebration of certain sacraments more appropriate at some times than others. The celebration of the Resurrection is the most fitting time to bring souls into the new life of Christ: “in the rite of Baptism death enters in by the slaying of sin, and the threefold immersion imitates the three days’ burial, while the rising from the water is like the rising from the tomb.” And for those who were for some reason unable to be baptized at Easter, Pentecost is appropriate as the feast of the Holy Spirit, and for the obvious reason that Scripture records St. Peter and the Apostles as having baptized three thousand people on that day.

Only for reasons of emergency should baptism be performed at other times than these. The same custom (that of the Roman see) must be observed everywhere for the sake of Christian unity. In a later letter to the bishops of southern Italy, Leo insists on the same point, with the particular detail that in this region baptisms were being done on the feasts of martyrs, and worse, without the proper period of preparation for catechumens.

It’s important to note that while infant baptism was certainly practiced in the ancient Church, in the fourth and fifth centuries there was also a fairly common practice of delaying baptism until later in life, even in practicing Christian families. One need only think of St. Monica, who did not allow her son St. Augustine to be baptized when he requested it as a boy, because she figured it was better for him to be baptized after he committed whatever sins he was likely going to be tempted to in his adolescence. (Obviously this was misguided, even if both Monica and Augustine had a happy ending.) Sts. Basil the Great and John Chrysostom were not baptized until after they finished their education.

More generally, there was a greater emphasis on conscious acceptance of the sacrament and repentance of past sins, given the number of people converting from paganism in the early centuries of the Church. Baptism was in general a more solemn and public ceremony, with a greater emphasis on the catechumenate, fasting, and other preparatory exercises than we are accustomed to today, when most baptisms are of infants with only a small group of people present. And so in this context we can understand why Leo thought it was gravely important for all baptisms to be administered at the appropriate solemn times, with Lent as the season of preparation—as indeed is standard today for converts.

Another sacramental innovation curbed by Leo was a practice introduced by some Italian bishops, who required those seeking the sacrament of penance to prove their sincerity by publicly giving a detailed list of their sins. Banning this practice, Leo pointed out that it doesn’t prove sincerity, since some sins are not that embarrassing to admit, while in other cases, someone who is truly penitent may not want to reveal his sins in public for reasons of either shame or liability. Leo wrote with sensitivity and realism:

The confession which is presented first to God and then to the bishop, who takes the part of an intercessor for the sins of penitents, is sufficient, for only if the sins of which the person who confesses is aware are not made known to the ears of the congregation will many be encouraged to perform penance.

So it is a myth that confession in the early Church was always done publicly.

In his letters addressing abuses, Leo could use stern words, but he would then turn on a dime and express his eagerness to punish only mildly or not at all, assuming the cooperation of the offending party.

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My sources on Pope St. Leo the Great have been these books:

• Trevor Jalland, The Life and Times of St. Leo the Great
• Philip Hughes, The Church in Crisis: A History of the General Councils, 325-1870
• Erick Ybarra, The Papacy: Revisiting the Debate between Catholics and Orthodox
• Pope St. Leo the Great, Sermons (CUA Press)
• Pope St. Leo the Great, Letters (CUA Press)

My quotations from Leo are not from one single translation, but are derived variously from these sources.