Letter XVII, dated July 15, 482 — the same day as Letter XVI — is the climactic letter of the Simplicius corpus. Where Letter XVI dealt with the Antiochene succession (the confirmation of Calendio) and rebuked Acacius for his silence, Letter XVII confronts the Alexandrian crisis that had been building since Timothy Salofaciolus’s death: the emperor is now proposing Peter Mongus — the man Simplicius had spent four years trying to have exiled — as the new bishop of Alexandria. The letter is the longest and most forceful of the late Simplicius correspondence, and it contains the most explicit exercise of Roman confirmatory jurisdiction in the entire corpus.

The confirmation passage is the editorial center of the letter. Simplicius describes a sequence: the Egyptian synod reports Timothy’s death and John’s election; the report is sent to Rome “as is customary” (ex more); Simplicius prepares to give the apostolic assent; and the election would thereby “receive its desired firmness by the assent of apostolic moderation.” The Latin is precise: apostolicae quoque moderationis assensu votivam sumeret firmitatem. The word quoque — “as well” — is the key: the election has already taken place, the synod has already reported, but the firmness the election desires (votivam firmitatem) requires something more — the Apostolic See’s assent. Without it, the election is formally incomplete. When the emperor’s letters arrive declaring John unworthy, Simplicius exercises the same jurisdiction in reverse: “Immediately I drew back my step and revoked my judgment concerning his confirmation.” The confirmation is Rome’s to give and Rome’s to withhold. The emperor provides testimony; the Roman bishop makes the judgment.

The astonishment that follows — that the emperor proposes Peter Mongus for the governance of Alexandria — brings the entire Simplicius correspondence to its crisis. Peter Mongus is the man whose exile Simplicius requested in Letter X, reiterated in Letter XI, pressed again in Letters XII and XIII, and whose continued presence in Alexandria Simplicius had warned would produce exactly this kind of outcome. In Letter XIV, Simplicius had told Zeno directly that if his earlier letters about Peter had been obeyed, the Antioch massacre would not have occurred. Now the same Peter — never exiled, never removed — is being proposed as bishop. Everything Simplicius warned against across five years of correspondence has come to pass, and the emperor is not merely failing to act but actively promoting the man Simplicius had been trying to remove.

The canonical argument against Peter’s promotion is one of the most carefully reasoned passages in the corpus. Simplicius does not simply reject Peter as a heretic; he distinguishes between reconciliation and promotion. Even if Peter now professes orthodoxy and seeks to return to Catholic communion, his path back must pass through satisfactio — the formal canonical process of making amends. A man undergoing satisfactio is a penitent, not a candidate for the episcopate. The hierarchy of reconciliation and the hierarchy of orders are distinct: one must first be reconciled before any question of promotion can arise, and a man with Peter’s history cannot be reconciled and promoted simultaneously. The argument is not rigid or punitive; it is structurally precise. Simplicius is not saying Peter can never return — he is saying Peter cannot return and ascend to the highest office in a single motion, because that would not be a genuine return but a seizure of power under the guise of reconciliation.

The commands to Acacius in the closing section represent the most direct exercise of papal authority over Constantinople in the Simplicius corpus. The verb is mandamus — “We command” — not the earlier hortamur (“We urge”) or precamur (“We pray”). Acacius is commanded to beseech the emperor unceasingly, to turn him from what is harmful, to inform him frequently “according to what We command,” and to report to Rome continually “what is done and what must be done — truthfully.” The addition of veraciter — “truthfully” — is new and pointed: Simplicius has not previously needed to specify that Acacius’s reports must be honest. The implication is that Simplicius suspects Acacius’s prior silence was not mere negligence but deliberate concealment of information Rome would not have wanted to hear.

The talent parable with which the letter closes frames Acacius’s entire responsibility in terms of eschatological accountability. The “talents entrusted to you by the Lord” are not Acacius’s own patriarchal authority but a stewardship for which he will render account. And the scope of that stewardship is not limited to Constantinople: Acacius must show himself faithful “not only in the Church over which you preside, but wherever you can, for Catholic unity and the definitions of the Fathers.” Simplicius is telling Acacius that his responsibility extends beyond his own see to the universal Church — which is the same principle that governs the Roman bishop’s own sollicitudo omnium ecclesiarum. The difference is that Acacius exercises this responsibility as a delegate; Simplicius exercises it as the one who delegated it. The letter ends, in effect, with a charge of universal scope given by the pope to the patriarch: do everything, everywhere, for the faith. And report to Us.

The reader who has followed the Simplicius corpus from Letter I to this point will recognize that Letter XVII is the moment when the cooperative framework that had sustained the Rome–Constantinople relationship since 477 reaches its breaking point. Simplicius is still writing as if the framework can hold — commanding, directing, expecting obedience. But the emperor is already proposing Peter Mongus, and Acacius’s silence has already signaled that Constantinople is no longer reliably executing Roman directives. Within months the Henoticon would be issued; within two years Acacius would be excommunicated; and the framework of these letters would give way to the thirty-five-year Acacian Schism. Letter XVII is the last full letter Simplicius wrote to Acacius in the surviving corpus. What follows in the PL is a Fragment of a letter to Zeno on the same Alexandrian question, and two further letters — but the relationship between Rome and Constantinople that these letters had sustained since 477 was, by this point, reaching its breaking point.