Letter CLXIII, dated March 28, 458 — one week after the March 21 cluster — is the fifth and final letter in the Atticus affair. It is addressed to Anatolius directly, returning to the bishop through whom Leo had been routing his directives since CLI, but now in a considerably sharper register. Anatolius has evidently written to Leo expressing displeasure at the repeated warnings he has received. Leo’s response is without apology.

The opening is among the most pointed in the entire Anatolius correspondence. Leo says he can see Anatolius is displeased with “the diligence of his solicitude” — using the precise term, sollicitudo, that defines his universal pastoral responsibility across the entire corpus. He does not respond to Anatolius’s displeasure by retreating or moderating his position; he defends the exercise of his solicitude as an act of fraternal charity demanded by the Lord’s commandment. More significantly, he does not address the question of whether he had the right to issue the directives he issued. That question is not engaged because it is not open: the exercise of the Roman bishop’s solicitude over the clergy of Constantinople is the premise of the correspondence, not a claim requiring fresh justification. Anatolius’s displeasure is noted and rebutted as a misunderstanding of Leo’s charitable intent; it does not touch the jurisdictional foundation from which the directives came.

Leo’s exposure of Atticus’s evasion is precise. Atticus’s written response had apparently claimed personal distaste for Eutyches — enough, Atticus thought, to signal orthodox sympathies without committing to a formal doctrinal condemnation. Leo identifies the evasion in a single sentence: personal quarrels exist even among Catholics; what is required is condemnation of the diabolical errors which the Catholic Faith condemns. These are categorically different things, and Atticus navigated between them deliberately. The evasion reflects an understanding of exactly what Leo’s requirement would demand — and a calculated attempt to satisfy the form of the requirement without its substance. Leo will not accept it.

The substantive requirement Leo finally imposes brings together three elements, each addressing a specific mode of evasion. First: Atticus must specify what he anathematizes in Eutyches — the condemnation must be doctrinal, not personal. Second: he must subscribe in writing by his own hand — the condemnation must be formally documented, not merely asserted verbally and informally. Third: the written subscription must be recited before the Christian people in the church itself — the recantation must be as public as the scandal it remedies. The precision of the three requirements is the precision of a legislator who has thought through every possible evasion and closed each one. The remedy is calibrated to the offense at every point.

The letter also contains a further articulation of the sealing-element formula that runs throughout this cluster. The definition Atticus must publicly profess is the one “to which your own charity subscribed and which the authority of the Apostolic See has confirmed.” The two acts are listed in order: Anatolius’s subscription as representative of the eastern episcopate; Rome’s confirmation as the sovereign, closing ratification. The Apostolic See’s confirmation is what renders the definition not merely received across the Church but irreversibly sealed. This formula — present also in Letters CLX and CLXII — is Leo’s consistent way of presenting the relationship between conciliar reception and Roman confirmation: the council defines and the episcopate subscribes; Rome confirms and the matter is closed.