The Council of Chalcedon (451 AD) is remembered above all for the highly controversial reception and enforcement of Pope Leo I of Rome’s Tome. For Chalcedonian Christians, Leo’s Tome came to be the definitive measure of Orthodoxy. Yet the way it was introduced and enforced at Chalcedon, and the theological content it contained, created deep tensions within the Church that have never fully healed. This article will first explain the historical context in which the Tome was presented at Chalcedon, especially the unprecedented way it was imposed as a standard of faith. It will then explore how Leo’s language differed from the earlier conciliar theology of St. Cyril of Alexandria and the First Council of Ephesus. Finally, it will examine key Christological problems perceived in the Tome’s teaching itself, and conclude by explaining why many ancient churches felt morally bound to reject Chalcedon largely on account of Leo’s Tome alone.
Novel Language Beyond Ephesus I (431)
It is crucial to emphasize that the First Council of Ephesus (431) was not simply Cyril’s personal theology but an Ecumenical Council received by both Eastern Orthodox and Oriental Orthodox Churches. Its Christology is, in substance, Miaphysite: the one incarnate Christ is a single Hypostasis (Person) and acting subject, in whom divinity and humanity are united without division. This reality is summed up in the conciliar and Cyrillian phrase “one nature of God the Word incarnate,” which in no way denies Christ’s full humanity, but safeguards the unity of His person. Any later Christological expression, therefore, must be measured against the faith already affirmed at Ephesus — not imposed above or in place of it.
St. Cyril of Alexandria, whose theology guided Ephesus I , taught that although Christ is “from two natures”, after the union we confess one Christ, one Lord, not “two natures” as the continuing mode of description (except in contemplation only), since that language risks dividing the acting subject. For this reason Cyril did not speak of Christ “in two natures” after the union.
Leo’s Tome, however, introduced precisely that phrasing. By teaching that Christ is to be acknowledged “in two natures,” it employed terminology unfamiliar — and troubling — to those formed by the Ephesian consensus. The later Chalcedonian Definition — “one person in two natures, unconfusedly, unchangeably, indivisibly, inseparably” — formalized this new direction. From a Miaphysite perspective, this was not merely a difference of emphasis, but a revision after the fact of the Christology already settled at an Ecumenical Council, effectively replacing the carefully‑won unity of 431 with a new Latin formula.
Clarification vs. Imposition
Before moving further, it is worth addressing a common defense of the Tome. Some argue: even if the language of “in two natures” was not used at Ephesus I, the Church was free to introduce it afterward to guard against Monophyistism. And this point, taken in itself, is of course true. The Church is not frozen in 431; She can clarify doctrine as errors arise. But such clarification must come by conciliar discernment and agreement, not by the unilateral imposition of one bishop’s letter as the standard of Orthodoxy. Even if Leo’s Tome contained no theological problems whatsoever, the method by which it was received at Chalcedon would still have been problematic: the bishops were expected to measure themselves by Leo’s Tome, rather than evaluate it in the light of the already‑received Christology of Ephesus I. This turned the normal conciliar process upside‑down. Instead of the council testing Leo, Leo effectively tested the council. That alone made many Eastern bishops uneasy — and rightly so.
The opposition was evident from the minutes of Chalcedon but was suppressed by fear and intimidation. It is deeply significant that the only bishop who dared openly to challenge the Tome itself — Patriarch Dioscorus of Alexandria — was deposed precisely for that reason. The main charge cited against him at Chalcedon was that he had broken communion with Leo (over the Tome) and had refused to read it at the Second Council of Ephesus (449). In other words, he was not condemned for teaching heresy of his own, but for refusing to endorse Leo’s formulation. The message sent to the Church was unmistakable: communion itself was to be conditioned upon acceptance of the Tome.
This desire of Rome to control the Church helps explain the later break between Rome and the Eastern Orthodox — the Great Schism of 1054 . Before Leo, Rome had not succeeded in imposing its own doctrinal language on the universal Church. When Pope Victor I (c. 189–198) attempted to excommunicate the Asian bishops over the Paschal question, he was rebuked by St. Irenaeus and others and forced to withdraw. Rome was honored, but it did not decide the faith of all. Against this backdrop, Leo’s insistence that his Tome be received as the binding measure of Orthodoxy marked a sharp departure from earlier conciliar humility and norm. The issue was not only what Leo said, but how Rome now expected its doctrinal formulations to be accepted. Chalcedon set a bad precedent: in 451 this unilateral approach fractured half the Church — and by 1054 the same unilateral approach of Rome introducing the filioque, caused the second major schism in the Church.
Christological Problems with Leo’s Tome
But as we will see, the Tome’s Christology itself raises far deeper concerns. It is worth quoting Leo’s language directly to see why many Cyrillians heard unmistakably Nestorian overtones in the Tome. The issue is not simply that Leo affirmed two natures — Cyril himself did so prior to the Incarnation as well as after the incarnation (in contemplation only after the incarnation). But Leo repeatedly attributes different actions, experiences, and even subjects to each nature, in a way that suggests two acting subjects standing alongside one another. This was perceived to be precisely the Nestorian pattern of thought itself — the very thing Cyril identified and condemned as dividing Christ into two acting subjects.
From a Miaphysite (and traditional Cyrillian) perspective the Tome’s Christology raised several theological problems:
Dividing Christ’s Acts Between Two Principles: Leo’s Tome famously taught that “Each nature performs what is proper to it in communion with the other; the Word performing what belongs to the Word, the flesh carrying out what belongs to the flesh.” While seemingly intending to preserve Christ’s full divinity and humanity, this statement alarmed Miaphysites. It appeared to split Christ’s life into two parallel sets of activities – miracles credited to His divinity, sufferings to His humanity. St. Cyril had explicitly condemned any such partition: “If anyone distributes between the two persons or hypostases the expressions…ascribes some to him as to a man separate from the Word…and others as befitting God to the Word, let him be anathema.” Cyril insisted that all Christ’s words and deeds are of one Person; he would not even allow language that sounded like two centers of action.
The Suffering of Christ and “Which Nature” on the Cross: The Tome’s language in places seemingly distances the divine Word from the sufferings of Jesus. Leo writes, “let him consider what nature it was that hung, pierced with nails, on the wood of the cross.” The intent was to refute any denial that Christ’s flesh was real and passible; yet by phrasing it as “which nature” was crucified, Leo’s letter gave the impression that the flesh (human nature) suffered apart from the divine nature. To Cyrillian eyes, this would have sounded improper. Without denying that the divinity is immortal/impassible, the proper way to speak of the Crucifixion, Cyril held, was that God the Word Himself suffered in the flesh – not that “a certain nature” suffered. This language is rooted directly in Scripture: “Therefore, since Christ suffered for us in the flesh…” (1 Peter 4:1), not “Christ’s human nature suffered”.
Condemnation of the “One Nature” Formula: Compounding Miaphysite dismay, Leo explicitly targeted the phrase “one nature” in Christ. In his rebuke of Eutyches, Leo wrote that “It is just as wicked to say that the only-begotten Son of God was of two natures before the incarnation as it is abominable to claim that there was a single nature in Him after the Word was made flesh.” This sweeping rejection of “one nature after the union” rang alarm bells. While Leo was aiming at the Eutychian idea that Christ’s humanity was absorbed or nullified, his words seemed to anathematize St. Cyril’s orthodox formula “mia physis tou Theou Logou sesarkōmenē” (“one nature of God the Word Incarnate”).
Nestorian Resonance and Reaction — with Explicit Nestorian Language: Perhaps the most troubling fact for those wary of Nestorianism was that Leo’s Tome did not merely lean Antiochene. It repeatedly speaks in a way that presupposes two different subjects acting in Christ – one divine, one human – instead of a single acting hypostasis of the Word. One of the clearest examples comes from Leo’s contrast between the One worshipped by the Magi and the One suffering on the Cross:
“He whom Herod treacherously endeavors to destroy is like ourselves in our earliest stage: but He whom the Magi delight to worship on their knees is the Lord of all.”
Here Leo is not even speaking about “natures” in the abstract. He is speaking about two He’s – two concrete subjects: one who is “like ourselves” (a merely human infant threatened by Herod), and another who is “the Lord of all” (the divine object of worship for the Magi). The sentence structure itself pulls the reader’s mind toward two different persons within Christ. This is not a clumsy way of saying that the one Lord is both God and man; it is practically textbook Nestorian two-subject Christology. This is miles away from the Cyrillian insistence that the Word Himself is the one and only acting subject of both worship and suffering.
Leo reinforces this same logic elsewhere when he writes:
For each form operates in communion with the other what is proper to it: the Word performing what belongs to the Word, and the flesh accomplishing what belongs to the flesh. One of these shines forth in miracles, the other succumbs to injuries.
In the above reference, Leo is not simply distinguishing two modes/natures of activity. He explicitly contrasts God the Word (the hypostasis) with His own flesh (the nature), as if the Word were one subject and His flesh another. This goes beyond assigning certain acts to divinity and others to humanity instead of the Person; it also effectively separates the Word from His flesh, which Cyril rejected.
Christ’s life is described as the alternating actions of two agents (God the Word and his flesh), rather than the single saving action of the Incarnate Logos. This is exactly the Nestorian pattern condemned by St. Cyril, who wrote:
“If anyone distributes between the two persons… some things to God, and others separately to the man… let him be anathema.”
Thus, the problem is not simply that Leo uses the phrase “in two natures,” his expressions suggest he thinks according to two acting subjects.
At this point some defenders of Leo will appeal to other sentences in the Tome – especially those in which Leo stresses that it is “one and the same” Christ such as:
“It is one and the same who is truly Son of God and truly Son of Man.”
But the mere repetition of oneness language does not dissolve the problem. The Nestorians themselves never claimed that Christ was “two persons” in the crude sense later attributed to them. Nestorius constantly emphasized the unity of Christ – but it was a unity of moral or volitional agreement between two subjects- a cooperation or conjunction, not the ontological unity of a single acting hypostasis. Thus, saying “it is one and the same” proves very little unless the underlying structure of thought is Cyrillian. Even Nestorians maintain there is only “one Christ”.
In a stunning irony, Nestorius himself – the deposed arch-heretic of 431 – reportedly “hailed [Leo’s Tome] as a vindication of his position.” This is noted explicitly by Karekin Sarkissian in The Council of Chalcedon and the Armenian Church, where he writes that “the Nestorian school could feel gratified, and the Tome of Leo…was hailed by Nestorius himself as a vindication of his position.” This fact was not lost on the Eastern churches. If the greatest opponent of Cyril rejoiced at Leo’s theology, how could they, as loyal Cyrillians, embrace it?
A Moral Obligation to Reject Chalcedon
In the wake of 451, numerous ancient churches notably in Egypt, Syria, Armenia, and Ethiopia – refused to receive the Council of Chalcedon. They did so not because they approved of Eutyches, but because they believed Chalcedon’s Tome of Leo had compromised the true faith. They saw themselves as guardians not only of St. Cyril’s legacy, but of the Ecumenical Council of Ephesus itself, forced to oppose a council that had, in their view, overstepped and “did violence” to the established theological tradition and sound Christology.
Miaphysite Patriarchs like Dioscorus of Alexandria and later Severus of Antioch rallied their flocks to hold fast to “the faith of Nicæa and Ephesus.” They considered the Tome’s teachings so problematic that they could not compromise without betraying divine truth. In their eyes, even if the Council of Chalcedon had the apparent backing of a large number of bishops (due to imperial force), its uncritical exaltation of Leo’s Tome meant the council had erred. The very purpose of an ecumenical council – to confirm the true faith – was, to them, sabotaged at Chalcedon.
In summary, the Tome of Leo became the lightning rod of controversy. Its imposition at Chalcedon without debate, discussion, or negotiation was unheard of, and its Christological content – however orthodox Rome claimed it was – struck Miaphysite Christians as theologically flawed or at least dangerously phrased. As a result, a significant portion of the ancient Church felt the duty to reject the Council of Chalcedon entirely, on the basis of Leo’s Tome alone. The enduring schism between the Chalcedonian churches and the Oriental Orthodox stands as historical testimony to how deeply Leo’s Tome was rejected.