Against Heresy

Pope Leo I was not only the theologian of the Tome but the doctrinal enforcer of Western orthodoxy, who hunted heresy with the same energy he brought to the Christological controversy. This file treats his three great anti-heretical campaigns: the prosecution of the Manichaeans at Rome (443–444), with the imperial edict that followed; the refutation of the Priscillianists in Ep. 15 to Turibius of Astorga (447); and his handling of the lingering residue of Pelagianism. It closes by showing that Leo’s polemic against heresy and his Christology were not two activities but one pastoral vocation — the guardianship of the rule of faith.

Tradition: Pan-Orthodox (Church Father / Latin)

The Doctrinal Enforcer of the West

Leo’s reputation rests on the Tome, but a pope of the fifth century did not separate dogma from discipline, and Leo’s pursuit of heresy was as deliberate and sustained as his defence of Chalcedon. He understood the bishop of Rome to be responsible for the integrity of the faith across the Latin churches, and he exercised that responsibility through preaching, through correspondence, through the convening of councils, and — where the secular law allowed — through the coercive arm of the Christian empire (Wessel, Leo the Great and the Spiritual Rebuilding of a Universal Rome, Leiden: Brill, 2008, 179–211; Neil, Leo the Great, London: Routledge, 2009, 28–35). Three movements illustrate this office: the Manichaeans, the Priscillianists, and the Pelagian remnant. In each Leo acts as the doctrinal enforcer of Western orthodoxy, and in each the content of his concern is finally Christological.

The Campaign Against the Manichaeans (443–444)

The most dramatic of these episodes was the campaign against the Manichaeans at Rome. Driven from Africa by the Vandal conquest, Manichaeans had fled to Rome and organized themselves secretly within the city; Leo learned of their presence around 443 and moved against them with notable thoroughness (Wessel, 179–211; Neil, 28–32). He had the leaders sought out and examined before a public assembly of clergy and senators, a deliberately public proceeding in which the sect’s secret rites were exposed — including the confessions, extracted at the trial, of a ritual abuse said to lie at the heart of the Manichaean “Elect” — and their sacred books were ordered burned (Leo, Sermon 16.4–5 and Sermon 24; Ep. 7, to the bishops of Italy; PL 54; trans. Feltoe, NPNF 2nd ser., vol. 12). Leo announced the result to the bishops of Italy in Ep. 7, warning them to be vigilant against Manichaeans who might have scattered to their own cities, and by early 444 he could present the sect as broken at Rome.

The campaign culminated in imperial legislation: Leo secured from Valentinian III an edict against the Manichaeans, issued 19 June 445, stripping them of civil rights and ordering their expulsion, which lent the force of Roman law to the bishop’s religious sentence (Wessel, 179–211; Neil, 28–32). The Manichaeans then become a recurring foil in Leo’s preaching: he warns against them in the Nativity sermons and the sermons on fasting, where their dualism and their docetic denial of Christ’s true flesh — the refusal to confess that the Word was born of the Virgin in a real human body — make them, for Leo, the photographic negative of the orthodoxy of the Tome (Leo, Sermons 22, 24, 34, 42; PL 54; trans. Feltoe). The anti-Manichaean polemic is thus not incidental to his Christology but its pastoral application: a man who fasts wrongly because he despises the body that Christ assumed is, in Leo’s eyes, a Manichaean in practice.

The Priscillianists and the Letter to Turibius (447)

In Spain Leo confronted Priscillianism, the ascetic and dualist movement descended from Priscillian of Avila (executed 385) that had proved unexpectedly durable in the Iberian churches. Turibius (Toribio), bishop of Astorga, alarmed at the sect’s spread, drew up a memorandum of its errors, circulated it to the Spanish bishops, and sent a copy to Rome. Leo replied with the long and systematic Letter 15, dated 21 July 447 (Leo, Ep. 15, to Turibius of Astorga; PL 54; trans. Feltoe, NPNF 2nd ser., vol. 12). The letter is a point-by-point refutation, organized as a series of chapters each answering a specific Priscillianist tenet: their dualism (an evil principle and an evil creator of the body), their use of astrology and fatalism, their resort to apocryphal scriptures in place of the canon, and their docetic Christology. Leo urges the Spanish episcopate to convene a general council of the province to root the sect out, and to examine whether any bishops were themselves tainted by it (Ep. 15, preface and §§16–17; Wessel, 195–211; Neil, 32–35).

The structural kinship between Priscillianism and Manichaeanism was not lost on Leo: both were, in his analysis, fundamentally dualist systems that disparaged the material creation and so corrupted the doctrine of the Incarnation at its root. To deny the goodness of the flesh was, by a short logical step, to deny that the Word had truly become flesh — and that denial was the very error the Tome existed to refute. Leo’s anti-Priscillianist letter is therefore continuous, in substance, with his Christological writing.

The Residue of Pelagianism

The third front was older and quieter: the residue of Pelagianism and its Caelestian offshoot, condemned in the previous generation but not wholly extinguished in the Western churches. Leo’s concern here was less the refutation of a living movement than the discipline of reconciliation — the proper terms on which clergy who had adhered to the Pelagian error might be received back into the Church. In one of his earliest letters as pope he rebuked the metropolitan of Aquileia for readmitting former Pelagian and Caelestian clergy too easily, and required that such men make an explicit and unambiguous condemnation of their former error before any restoration, lest a lax reconciliation let the heresy seep back under cover of charity (Leo, Ep. 1 and Ep. 2, to the bishops of the province of Aquileia; PL 54; trans. Feltoe; Neil, 30–32; Jalland, The Life and Times of St. Leo the Great, London: SPCK, 1941, 71–78). The episode shows Leo’s administrative cast of mind applied to doctrine: heresy is defeated not only by argument but by the careful regulation of the Church’s discipline of repentance and re-entry, so that orthodoxy is guarded at the threshold.

One Pastoral Vocation

The three campaigns are usually catalogued separately, but for Leo they were a single work. The thread that binds the Manichaean, the Priscillianist, and the Pelagian to the Christological controversy is the doctrine of the Incarnation. The Manichaeans and Priscillianists denied the goodness of the flesh and so the reality of Christ’s body; the Pelagians, by exaggerating the unaided power of human nature, undercut the necessity of the grace that the Incarnation brought; Eutyches and Nestorius, against whom the Tome was written, divided or confused the natures of the one Christ. In every case the stake is the same — whether the Word was truly made flesh, fully God and fully man, for the salvation of a real human nature (Wessel, 179–211; Neil, 28–35). Leo’s guardianship of Western doctrinal order and his Christology are therefore one pastoral vocation: the bishop’s duty to keep whole the confession that the eternal Son took our complete humanity. The polemicist who burned the Manichaeans’ books and the theologian who wrote the Tome are the same man, defending the same mystery from opposite sides — and that unity is the key to reading Leo’s anti-heretical labour not as the harshness of an inquisitor but as the vigilance of a pastor over the rule of faith.

See Also

• The Letters and Church Order — the correspondence and administrative machinery through which the campaigns were waged
• The Tome to Flavian — the Christology that Leo’s anti-heretical work defends
• Preaching the Mystery — the Nativity and Lenten sermons that warn against Manichaean dualism
• The Man and the Office — Leo’s self-understanding as guardian of the Western churches
• Church Fathers — the patristic refutation of heresy as a genre

References

• Leo I, Epistolae and Sermones, PL 54; trans. Charles Lett Feltoe, Letters and Sermons of Leo the Great, NPNF 2nd ser., vol. 12 (Oxford/New York, 1895); trans. Edmund Hunt, St. Leo the Great: Letters, Fathers of the Church 34 (Washington, DC: CUA Press, 1957).
• Leo I, Ep. 7 (to the bishops of Italy, on the Manichaeans); Ep. 15 (to Turibius of Astorga, 21 July 447); Ep. 1–2 (to the province of Aquileia, on Pelagian clergy), PL 54.
• Valentinian III, edict against the Manichaeans, 19 June 445.
• Susan Wessel, Leo the Great and the Spiritual Rebuilding of a Universal Rome (Leiden: Brill, 2008).
• Bronwen Neil, Leo the Great (London: Routledge, 2009).
• Trevor G. Jalland, The Life and Times of St. Leo the Great (London: SPCK, 1941).