Letter XC is Leo’s formal consent to the Council of Chalcedon proceeding as Marcian has arranged — a consent that comes with two governing conditions stated plainly: the faith is not doubtful and is not to be debated as such, and the Nicene decrees are not to be disturbed. Chalcedon will operate within the framework the Apostolic See has defined; it will not generate a new framework through free deliberation. The consent is real, but it is consent to something specific, not a blank authorization for the assembled bishops to determine the outcome.

The characterization of Ephesus II in Chapter I is the sharpest in the corpus. In Letter LXXXV Leo said it had “neither the name nor the merit of a synod”; here he states the reason explicitly: it was “manifestly conducted to subvert the faith.” The invalidity is not procedural but teleological — a gathering assembled for the purpose of destroying what it was supposed to uphold cannot claim conciliar authority. And Leo then notes that Marcian has annulled it. This is a remarkable chain: Leo declares Ephesus II invalid; Marcian, aligning himself with Leo’s position, decrees it annulled and authorizes Chalcedon in its place. The annulment of one imperial council and the authorization of another follow from Rome’s governing determination. Imperial authority executes what the Apostolic See has declared.

The personal statement of Chapter II — “my presence is to be reckoned in the brothers I sent” — is Leo’s most direct articulation of the vice mea principle in the entire corpus. He is not describing a delegation of authority to representatives who will act on his behalf with some degree of independence. He is saying that what happens at Chalcedon through Paschasinus and his colleagues is what happens through him. His presence is there. The council that meets is not a gathering from which Leo is absent; it is a gathering over which Leo presides through the persons he has placed there in his stead. This is the Apostolic See’s governance of the universal Church operating at the highest institutional level: the most important council of the century, presided over by the Roman bishop through his legates, defining the faith within the framework Rome has established.

The connection between Letter XC and the opening of Chalcedon is direct and concrete, and the primary source is now before us. When the Council convened in October 451, Paschasinus opened the first session by announcing that Dioscorus was not to be allowed a seat in the assembly — describing Leo as “the most blessed and apostolic bishop of the Roman city, which is the head of all the churches.” When the imperial judges pressed the legates to state the specific charge against Dioscorus, it was Lucentius — Leo’s other legate — who answered with a two-part indictment: “He undertook to give sentence against one over whom he had no jurisdiction. And he dared to hold a synod without the authority of the Apostolic See, a thing which had never taken place nor can take place.” The two charges are inseparable: Dioscorus had exceeded his jurisdiction in condemning Flavian, and he had presided over a council without Rome’s authority — a thing that had never happened and, Lucentius asserts, cannot happen. Dioscorus’s disqualification from sitting at Chalcedon derived directly from both offenses. Letter XC — Leo consenting to Chalcedon under defined conditions, insisting the faith is not doubtful, declaring his presence in his legates — is the letter that makes the operating premise of that opening session visible. The council proceeded on Rome’s authorization; the man who had acted without it was removed before it could begin. The full documentation of Chalcedon’s proceedings will be examined when those letters arrive in this corpus.