Letter XXXIII is the only letter of the June 13, 449 cluster addressed to the council itself. Leo is writing to the Second Synod of Ephesus — the gathering that would convene on August 1, 449, and that he would later describe in the most devastating terms in his arsenal: a latrocinium, a den of robbers. At the time of writing, he does not know this. He is dispatching the letter with genuine expectations: that his legates will present the Tome, that Eutyches will be held to his written promise of submission, and that the council will confirm the condemnation of the previous year. None of this happened. The reader of this letter should hold both things simultaneously — the confidence of Leo’s directions and the catastrophe that awaited them — because the contrast illuminates what the letter shows about his understanding of his authority.

Chapter I opens with a description of the emperor that is simultaneously a compliment and a theology of the papacy. Theodosius II, Leo writes, has brought to bear the authority of the Apostolic See “as if wishing to have declared by the most blessed Peter himself what is to be praised in his confession.” The emperor’s act of convening a council and invoking Rome’s authority is described not as a political maneuver but as a recognition of what the Apostolic See is: the continuing voice of Peter. The reader who has followed the Petrine theology from Letters IX and X through Letter XXVIII will recognize the structure immediately. Peter’s confession at Caesarea Philippi is the foundation of the Church; the Apostolic See perpetuates Peter’s authority; therefore, to invoke the Apostolic See is to invoke Peter. Leo does not state this as his own claim here — he attributes the recognition to the emperor, which gives it a different rhetorical weight. Even the Christian emperor, in Leo’s account, understands the papacy in Petrine terms.

The theological centerpiece of Chapter I is Leo’s reading of Matt. 16:13–18. He has Peter’s brief confession — “You are the Christ, the Son of the living God” — yield the full two-nature Christology: true in Deity, true in flesh, with the property of the twofold nature preserved intact, both one. The phrase utrumque unus — both, one — is as compressed as the Tome is expansive. Everything the Tome argues in the technical vocabulary of the two natures is already present, Leo insists, in what Peter said at Caesarea Philippi. The council is not being asked to innovate or to adjudicate between competing theological proposals; it is being asked to receive what Peter already confessed. This framing is deliberate and significant: the authority invoked is not conciliar precedent but apostolic confession, and the mediator of that confession is the Apostolic See.

Chapter II establishes the council’s agenda in two stages: first condemnation, then restoration. The delegation formula — “to attend in my stead the holy assembly of your brotherhood” — is the vice mea formula that runs through the June 13 cluster. Leo’s legates do not advise the council; they represent Leo’s presence and authority within it. The reference to Eutyches’s libellus is equally precise: Eutyches has already promised, in a formal written submission to Rome, to follow Leo’s judgment in all things. The council can hold him to this. The implication is clear — the Apostolic See has already received Eutyches’s acknowledgment of its authority to decide the case, and the council is now being asked to act on the terms of that submission. The closing reference to the Tome (“we have written back to him more fully”) positions the doctrinal foundation of the council’s work as a document that has come from Rome to Flavian. The council acts in the light of what Rome has already declared.

The gap between what Letter XXXIII directs and what Ephesus II produced is one of the most instructive episodes in the Leo corpus. Dioscorus of Alexandria presided over a council that refused to hear Leo’s legates, restored Eutyches without requiring his repentance, and deposed Flavian — who died shortly afterward, possibly from injuries sustained at the council. Leo’s deacon Hilarus escaped and sent back to Rome a single Greek word: contradicitur — it has been opposed. The Tome was never read. Every element of Letter XXXIII’s agenda was reversed. What followed — Leo’s refusal to accept the council’s acts, his relentless pressure on the emperor and empress, and ultimately the Council of Chalcedon in 451 — was the direct consequence of this disaster. At Chalcedon, Letter XXXIII was finally fulfilled: the error was condemned, the Tome was received, and the Petrine confession of Chapter I was proclaimed as the standard by which the faith had been judged. The delegates of the Eastern churches, hearing the Tome read aloud, cried: “Peter has spoken through Leo.”