Letter C is one of three documents sent to Leo in the weeks following Chalcedon all pressing the same request: the confirmation of Canon 28. The Council of Chalcedon made the request in Letter XCVIII; Emperor Marcian makes it here in Letter C; Anatolius of Constantinople will make it again in Letter CI. The reader who comes to these letters in sequence will recognize a sustained, coordinated appeal — backed by the full institutional weight of the fifth-century world — directed at a single point of authority whose confirmation was understood to be necessary. That understanding is the primacy argument made visible from the outside.

Chapter II contains the most important single sentence in the letter for this project’s purposes. Marcian tells Leo that at Chalcedon, “all assented to the exposition in accordance with the letter of your holiness, as truth required.” This is the emperor of the Roman world describing the Council of Chalcedon’s doctrinal process. The bishops did not deliberate independently and arrive at a conclusion that happened to match Leo’s Tome; they assented to an exposition measured against Leo’s letter as its standard. The formulation is substantively identical to what Chalcedon’s own synodal letter stated in theological terms — that Leo was established as the interpreter of Peter’s voice for all, and that his letter had been used as the doctrinal norm — but it comes here from the secular imperial authority. Emperor and council alike describe the same reality: Leo’s letter was the measure.

Chapter III is where the Canon 28 request is stated in its imperial form, and the reader should attend to what Marcian acknowledges in the act of asking. He notes that Leo’s legates “vehemently prohibited anything being decreed by the synod concerning this venerable Church” — that is, Paschasinus, Lucentius, and Bonifacius formally objected to Canon 28 at the council. Marcian is aware of the opposition; he asks Leo to override his own legates’ position and grant consent. The request is framed as diplomatically as possible — Constantinople is the New Rome; the same honor was decreed by the holy synod and by the 150 Fathers under Theodosius — but the structure of the request is unambiguous. It is Leo’s consent that is wanted, Leo’s command that is sought, and Leo’s legates whose objection needs to be set aside. No such request would be directed at Leo if his judgment were not operative.

The Canon 28 question is now fully assembled. Three separate appeals — from Chalcedon’s five hundred bishops (Letter XCVIII), from Emperor Marcian (Letter C), and from Anatolius of Constantinople (Letter CI) — converge on the same point. Leo’s responses come in two letters, each addressed to the appellant most directly implicated. Letter CIV is his reply to Marcian, and it addresses the ecclesiological foundation: Constantinople is a royal city but cannot make itself an Apostolic See. “One loses what is proper by coveting what is undue.” The Nicene canons cannot be overturned by any audacity, and Leo’s own stewardship before God does not permit him to prioritize one brother’s ambition over the universal Church’s common good — framing his rejection not as a matter of preference but as a matter of accountability. Letter CVI is his reply to Anatolius, and it is the most comprehensive canonical statement in the entire Canon 28 exchange. Leo makes three arguments that the reader should hold together. First: the Constantinople I canons of 381 were never sent to the Apostolic See — “never sent to the Apostolic See’s notice by your predecessors,” Leo writes — which confirms from Leo’s own pen what the XCVIII Commentary observed: Canon 3 of 381 was never formally received by Rome, and Anatolius is attempting to prop up “a long-fallen and now useless structure with late, futile supports.” Second: no gathering of bishops, however large, can override Nicaea — “no number of bishops, however large, dare compare or prefer itself to Nicaea’s three hundred eighteen, so divinely privileged that any ecclesiastical judgments, by fewer or more, contrary to their constitutions, are wholly void.” This is Leo’s direct answer to the weight-of-numbers argument implicit in invoking five hundred assembled bishops: the number is irrelevant when the act is contrary to Nicaea. Third: Leo’s legates were right. Anatolius had complained about Paschasinus and Lucentius’s opposition; Leo tells him that their opposition “commends them to me, but accuses you.” The formal apostolic nullification then follows in Letter CV, grounded in the authority of the blessed apostle Peter and issued as a universal judgment. Taken together — CIV, CVI, and CV — Leo’s response to the three-part Canon 28 appeal shows him operating simultaneously as a canonical judge, a theological reasoner, and an apostolic authority: three modes of a single office, each brought to bear on the same question from a different angle.