Pope Saint Leo the Great (440-461)

The pope of Chalcedon

The central dossier of Leo is the crisis opened by Eutyches, a monk of Constantinople, after the Council of Ephesus. To avoid the Nestorian division of Christ into two subjects, Eutyches refuses to confess clearly the permanence of the two natures after the Incarnation. The Catholic faith must then hold together two truths: Christ is one single Son, not two persons; he is also true God and true man, without the humanity being absorbed by the divinity.^[4][5]

Leo answers with the dogmatic letter to Flavian of Constantinople of 13 June 449, called the Tome to Flavian. The text is not an abstract speculation: it starts from the Creed, the Scriptures and the economy of salvation. If the Word has not taken our real nature, he does not really heal our nature. If Christ is only a man united to God, he does not save as God. The pope therefore lays down the grammar that will allow Chalcedon to confess one and the same Christ "in two natures".^[6]

The Tome confesses a true God born in an entire and perfect human nature: fully God by what is his, fully man by what is ours, sin excepted (paraphrase)^[7].

The doctor of the Roman primacy

Leo does not invent the Roman primacy: the neighbouring articles already show Clement, Victor, Stephen, Julius, Damasus, Siricius, Innocent, Zosimus, Boniface, Celestine and Sixtus III acting as bishops of a see to which judgment and communion are requested. But Leo gives this consciousness a theological expression of a new breadth.^[8][9]

In his anniversary sermons, he affirms that Peter does not cease to act in the see he received. This idea is not a personal triumph of Leo. On the contrary, it founds the humility of the minister: what is well decreed by the bishop of Rome comes from the work of Christ and the Petrine charge, not from a human prestige.

In his Sermon 3, preached for the anniversary of his elevation to the pontificate, Leo refers to Peter — whose power remains alive in his see — all the good his ministry accomplishes (paraphrase)^[10].

The pastor of a Rome in crisis

The fifth century is not an age of stability. The Vandals occupy Latin Africa, refugees arrive in Rome, Western imperial authority weakens, the Huns enter Italy, and doctrinal controversies tear the Churches apart. Benedict XVI stresses that these circumstances oblige the bishop of Rome to play a more visible civil and political role, without that role replacing his proper ministry.^[11]

Leo then preaches with a rare density. The Catholic Encyclopedia counts 96 authentic sermons and 143 preserved letters, to which are added thirty letters addressed to him.^[12] These texts show a pope who speaks to the people, corrects bishops, answers emperors, instructs the faithful, organises almsgiving, denounces superstitions and constantly links doctrine to moral life.

The Holy See and the official chronology

The official record of the Holy See gives the soberest markers: 45th pope, beginning of the pontificate on 29 September 440, end on 10 November 461, birth in Tuscany.^[13] The chronology matches the historical notices: Sixtus III dies on 19 August 440; Leo is then in Gaul on a peacemaking mission between Aetius and Albinus; he returns to Rome and receives episcopal consecration on 29 September.^[14]

This initial situation announces the whole pontificate. Leo does not come to the see of Peter as an unknown shut away in the Roman offices. He is already a leading deacon, recognised enough to be sent by the imperial court into a major political conflict.

The Liber Pontificalis

The Liber Pontificalis presents him as originating from Tuscany, son of Quintianus, and attributes to him a pontificate of 21 years, 1 month and 13 days.^[15] As always in the ancient notices, the exact figures must be checked against modern lists; but the information on the Tuscan origin and the father Quintianus is found again in ancient and modern syntheses.

The same notice stresses ordinations, buildings and burial. It places Leo in the memory of a Rome that builds: restorations, basilicas, links with Saint Peter and Saint Paul. The doctrinal pope of Chalcedon is also a pope of stones, holy places and Christian visibility in the city.

The sermons and the letters

The sermons are essential because they are the first papal preachings preserved in so ample a corpus. Benedict XVI notes that Leo is the first pope whose preaching to the people has come down to us in substantial form.^[16] They cover Christmas, Epiphany, Lent, Easter, the Passion, the Ascension, Pentecost, the Ember-Day fasts, ordination anniversaries and the feast of the apostles Peter and Paul.

The letters, for their part, show government at work. They go from Italy to Gaul, from Spain to Africa, from Thessalonica to Alexandria, from Constantinople to the emperors. They make it possible to follow a pontificate not through anecdotes, but through dated dossiers: Pelagians of Aquileia, Manichaeans of Rome, Priscillianists of Spain, Hilary of Arles, Anastasius of Thessalonica, Dioscorus of Alexandria, Flavian, Theodosius II, Pulcheria, Marcian, Anatolius.

A Roman deacon already known outside Rome

The first certain information presents Leo as a deacon of the Roman Church under Celestine I. The Catholic Encyclopedia notes that he is already known outside Rome: John Cassian dedicates to him around 430-431 the treatise De Incarnatione Domini contra Nestorium, written against Nestorius at the request of the archdeacon Leo.^[17]

This detail matters. Before being the pope of Chalcedon, Leo is already engaged in the doctrinal battle against Christological errors. He does not discover the dossier in 449; he has belonged since the 430s to the Roman network defending the personal unity of Christ against Nestorius.

The mission to Gaul and the election

Under Sixtus III, Emperor Valentinian III sends Leo to Gaul to reconcile Aetius, the military commander, and Albinus, a high magistrate. The mission reveals the confidence of the imperial court in the Roman deacon.^[18]

Sixtus III dies during this absence. Leo learns of his election in Gaul, returns to Rome, then is consecrated on 29 September 440.^[19] The beginning of his pontificate is therefore marked by a rare trait: the man who will become the great theologian of Christ is also a public negotiator, capable of acting when civil peace threatens to break.

The Pelagians of Aquileia

Shortly after his election, Leo learns through Septimus of Altinum that clerics linked to Pelagius are admitted to communion at Aquileia without explicit abjuration. The pope calls for a provincial synod and demands an unambiguous confession of faith.^[20]

The decision continues the line of Innocent I, Zosimus, Boniface I and Celestine I: grace is not a decorative supplement added to human freedom; it is the interior help without which wounded man cannot accomplish salvific good. Leo therefore does not let Pelagianism survive as a mere moral opinion.

The Manichaeans at Rome

The Manichaean dossier is more visible still. Manichaeans driven out of Africa by the Vandals settle in Rome and form a clandestine community there. Leo orders the faithful to report them to the priests; in 443, with senators and presbyters, he personally conducts an inquiry. Several are converted and admitted to confession; the obstinate are banished by the civil authorities under the imperial edicts.^[21]

This firmness is not a police obsession. Manichaeism disfigures creation, the body, marriage, the Incarnation and moral responsibility. In a city already weakened by famines and refugees, Leo understands that doctrinal error also produces a spiritual disorganisation of the people.

The Priscillianists of Spain

In Spain, Bishop Turibius of Astorga informs Leo of the persistence of Priscillianism. The pope answers with a long letter refuting the errors and asks for the convocation of a regional synod; if a general council of the Spanish bishops is impossible, at least the bishops of Galicia must meet.^[22]

The Spanish case shows the Leonine method: local inquiry, doctrinal letter, synodal convocation, precise correction. Rome does not replace the bishops; it obliges them not to let error settle in through inertia.

Hilary of Arles and the Gallican vicariate

Gaul poses Leo a problem of government. The preceding popes had made Arles a regional Roman relay, but Bishop Hilary of Arles exercises his authority excessively. He deposes Celidonius of Besancon; the latter appeals to Rome. Hilary also consecrates a bishop in place of Projectus, still living. Leo gathers a Roman synod around 445, restores Celidonius, restores Projectus, then withdraws from Hilary part of his metropolitan rights.^[23]

This conflict is delicate because Hilary is a saint. Leo does not treat him as an enemy of the Church; after his death in 449, he even designates him as of "blessed memory". But personal holiness does not give the right to overturn the canons. The Roman primacy serves here to protect unjustly deposed bishops and to prevent a regional centre from turning into an arbitrary power.

The edict of Valentinian III

On 8 July 445, Valentinian III backs the decisions of Leo concerning Hilary and solemnly recognises the primacy of the bishop of Rome over the Church. The Catholic Encyclopedia sees in this a significant moment: the spiritual authority of Leo receives imperial support in a context of provincial disorder.^[24]

This edict must be read correctly. The emperor does not create the primacy of Peter; he juridically recognises, in the Roman civil order, an ecclesial authority that Leo founds theologically on the apostolic see. The distinction matters to avoid two errors: reducing the primacy to a political favour, or acting as if the ancient Church operated outside any imperial framework.

Thessalonica and Illyricum

Leo also reorganises the vicariate of Thessalonica for Eastern Illyricum, a region politically tied to the Eastern Empire but historically attached to Roman jurisdiction. He entrusts this charge to Anastasius of Thessalonica, then sharply recalls him to order when the latter acts harshly and arbitrarily.^[25]

The parallel with Arles is striking: Leo uses local relays, but refuses to let them become independent of Rome or oppressive toward bishops. His centralisation is not the suppression of mediations; it is the control of a communion at risk of fragmenting.

Vandal Africa

After the Vandal conquest, Latin Africa finds itself in a dark situation. Leo sends the Roman priest Potentius to gather information on the spot, then addresses detailed disciplinary instructions to the African bishops.^[26] The gesture continues the old relationship between Rome and the Africa of Augustine, but in an overturned world: Carthage is no longer only a great conciliar centre; it is under Vandal Arian pressure.

This African attention recalls that the pope of Chalcedon is not absorbed by the East. He keeps his eyes on the Latin provinces, on the Churches destabilised by the migrations and on the concrete discipline of the sacraments.

Eutyches and the fear of Nestorius

Eutyches wants to defend the unity of Christ against Nestorius. His intention may seem orthodox at first; his vocabulary becomes dangerous when he refuses to affirm that the humanity of Christ remains fully consubstantial with ours after the union. A Christology that protects unity by effacing humanity ends up losing concrete salvation: God does not save a humanity he would not really have assumed.

The Tome answers point by point. Leo shows in it that the Creed already suffices to overturn the heresies: the eternal Son is born of the Father before all ages, and this same Son is born in time of the Virgin Mary. The Incarnation does not change God into a creature; it unites without confusion the divine nature and the human nature in the one person of the Word.^[27]

Leo explains in it that this birth in time neither takes away nor adds anything to the eternal generation of the Son: it is wholly ordered to raising up man deceived by the seducer (paraphrase)^[28].

"Each form accomplishes what is proper to it"

The most famous sentence of the Tome becomes an axis of Chalcedonian doctrine: each nature acts according to what is proper to it, in communion with the other. Leo does not say that two persons act side by side; he says that one single Christ acts truly according to his divinity and truly according to his humanity.

The most famous formula of the Tome distinguishes the two actings united in the one Christ: to the Word the divine works, to the assumed flesh the human works, without separating the subject who acts (paraphrase)^[29].

This formula makes it possible to read the Gospel without mutilation. Christ sleeps, weeps, suffers, dies: these are really human acts. He forgives sins, walks on the sea, raises the dead, opens paradise: these are divine acts. But the one who does all this is one and the same Lord Jesus Christ.

A doctrine of salvation, not only a formula

Leo insists: Christ is complete in what is his and complete in what is ours, sin excepted. He takes the form of a servant without stain; he increases the human without diminishing the divine.^[30] Christology is therefore directly soteriological. If the truth of God in Christ is weakened, salvation loses its power; if the truth of man in Christ is weakened, salvation no longer touches our condition.

This doctrine joins the classic phrase of the Fathers: what is not assumed is not healed. Leo does not quote it in this form, but his whole reasoning presupposes it. The Word heals man by really assuming man.

From the Robber Council of Ephesus to the council of 451

In 449, the council dominated by Dioscorus of Alexandria rehabilitates Eutyches and deposes Flavian. Leo will call it the "Robber Council of Ephesus". He then writes to Constantinople, to Theodosius II, to Pulcheria, then seeks the support of Valentinian III and Galla Placidia to obtain a true council.^[31]

After the death of Theodosius II, Marcian convokes the Council of Chalcedon in 451. The Roman legates represent Leo there. The council receives the doctrine of the Tome and formulates the definition of faith that will become one of the pillars of Catholic Christology.

The definition of the two natures

Chalcedon confesses one and the same Christ, perfect in divinity and perfect in humanity, true God and true man, consubstantial with the Father according to divinity and consubstantial with us according to humanity, acknowledged in two natures, without confusion, without change, without division, without separation.^[32]

"One and the same Christ, Son, Lord, Only-begotten, acknowledged in two natures, without confusion, without change, without division, without separation." — Council of Chalcedon, definition of faith, 451^[33]

The reception of the Tome

Benedict XVI recalls that the acts of the council preserve the famous acclamation: "Peter has spoken through the mouth of Leo".^[34] This formula does not mean that every private sentence of a pope would automatically be a dogmatic definition. It means that at that precise moment, in that doctrinal letter received by the council, the bishops recognise the apostolic faith of Peter expressed by his successor.

Leo does not accept all of Chalcedon without reservation. He approves the definition of faith, but rejects canon 28, which attributed to Constantinople a privileged place on the grounds that it was the "New Rome". For Leo, primacy does not come from the political greatness of a capital; it comes from the confession of Peter and apostolic succession.^[35][36]

Christmas: Christian dignity and new life

Leo is not only a jurist of the Church. His Christmas sermons are among the strongest spiritual texts of Latin antiquity. He starts from the mystery of the Word made flesh to call the baptised to live according to the dignity received.

Leo urges the faithful to remember the Head and the Body of which they are members: snatched from the power of darkness, they have been transferred into the light and the kingdom of God (paraphrase)^[37].

The point is typically Leonine: doctrine becomes moral without becoming moralism. Because the Son has taken our nature, the Christian can no longer live as if his body, his soul, his acts and his charity were indifferent.

Liturgy and the present of the mystery

Benedict XVI stresses another intuition of Leo: the liturgy is not a simple memory of the past, but the actualisation of invisible realities acting in the life of the Christian.^[38] In his sermons, Easter, Christmas, the Passion and the fasts are not psychological anniversaries; they make the mystery of Christ present to the Church.

This liturgical theology explains why Leo constantly links fasting to almsgiving, feast to forgiveness, contemplation of Christ to conversion of morals. Christian worship is true only if it shapes a Christian life.

Peter and Paul, Roman roots

In sermon 82, Leo meditates on the apostles Peter and Paul at Rome. Peter carried the trophy of the Cross into the citadel of the Empire; Paul, the vessel of election, was associated with him under Nero.^[39]

Addressing Peter, Leo sees in his coming to Rome, by divine disposition, the meeting of a great honour of power and a great glory of suffering (paraphrase)^[40].

Rome is therefore not great first because it was the imperial capital. It is great because it received the blood of Peter and Paul. It is this spiritual reading of the city that founds the Roman consciousness of Leo.

The encounter with Attila in 452

In 452, Attila ravages northern Italy. At the emperor's request, Leo sets out with the consul Avienus and the prefect Trigetius to meet the Hun chief near the Mincio, in the region of Mantua. The Catholic Encyclopedia reports that he obtains from Attila the promise to withdraw from Italy and to negotiate peace with the emperor.^[41]

Benedict XVI sees in this an event become emblematic of pontifical action for peace.^[42] One must remain sober: historians discuss the military, sanitary, logistical and political factors that weighed on the retreat of Attila. But the mission of Leo remains a major fact: in a West where imperial authority is coming apart, the pope appears as a public intercessor in the name of Rome.

Genseric and the sack of Rome in 455

Three years later, Genseric and the Vandals enter Rome. Leo does not succeed in preventing the sack, which lasts two weeks; but his intervention obtains that the city not be burned, that the inhabitants be spared as much as possible, and that the basilicas of Saint Peter, Saint Paul and Saint John serve as places of refuge.^[43][44]

This difference between 452 and 455 is spiritually important. The holiness of Leo does not mean spectacular effectiveness in every crisis. Sometimes he stops the enemy; sometimes he only limits the evil. In both cases, he acts as pastor of an exposed people.

Saint Paul Outside the Walls and Saint Peter

Leo restores and embellishes several Roman places. After the destruction of the roof of Saint Paul Outside the Walls by lightning, he has it replaced; he also contributes to the improvements of the basilica, while the triumphal arch preserves the memory of Galla Placidia.^[45][46]

He also restores Saint Peter at the Vatican, and tradition preserves his link with the basilica where his relics rest today. In Leo, visible stone serves a catechesis: Rome reads as an apostolic city, memory of the martyrs and centre of communion.

The burial at Saint Peter

Leo dies on 10 November 461. The Catholic Encyclopedia indicates that he was first buried in the vestibule of Saint Peter; in 688, Pope Sergius transferred his remains inside the basilica and had a special altar established. His relics rest today beneath the altar dedicated to him.^[47]

This burial expresses the place of Leo in Catholic memory: not only doctor of Chalcedon, but Roman witness of the Petrine succession at the very foot of the tomb of Peter.

Doctor of the Church

In 1754, Benedict XIV proclaims Leo a Doctor of the Church.^[58] This title recognises the doctrinal scope of his sermons and letters, above all in the confession of Christ. Leo therefore belongs to the small number of popes whose personal teaching has become a major doctrinal reference for the whole Church.

His doctrine is not only historical. The Catechism of the Catholic Church cites the Chalcedonian tradition to confess that Christ is true God and true man, and that the union of the two natures takes place in the one person of the Son.^[59] The language of Leo remains behind this grammar.

A model of primacy as service

Leo is sometimes used as a blunt argument in debates on the papacy. The article must avoid reducing him to a slogan. His primacy is real, strong, sometimes very firm; but it always unfolds in concrete dossiers: protecting wronged bishops, having a heresy judged, keeping a province in communion, confirming a council, defending the people of Rome.

The best summary is that of Benedict XVI: Leo exercises primacy in West and East with prudence, firmness and lucidity, to serve effectively the communion of the one Church of Christ.^[60]

• Council of Chalcedon (451) — conciliar reception of the Tome to Flavian and definition of the two natures of Christ.
• The Monophysite crisis — doctrinal context of Eutyches, Dioscorus, Flavian and Chalcedon.
• The Incarnation and the Cross — salvific scope of Chalcedonian Christology.
• Pope Saint Sixtus III — immediate predecessor, pope of the reception of Ephesus and of Saint Mary Major.
• Pope Saint Celestine I — pope of the Roman synod against Nestorius and of the Council of Ephesus.
• Pope Saint Zosimus — earlier milestone in the struggle against Pelagianism and jurisdictional tensions.
• Basilica of Saint Paul Outside the Walls — basilica restored and embellished under Leo.
• Orthodoxy — context of the Eastern reception, of Chalcedon and of canon 28.