Letter XV is the companion to Letter XIV, forming the same coordinated pair that Letters XII and XIII had formed for the Peter Mongus exile request: Simplicius writes to the emperor and to the patriarch about the same matter, with the letter to the patriarch carrying the more direct and nuanced address. Where Letter XIV to Zeno praised the emperor’s punishment of the perpetrators and named Peter as the guarantor of his pledge, Letter XV to Acacius addresses the intermediary who was both the executor of the irregular ordination and the channel through whom Simplicius’s earlier exile requests should have reached the emperor. The letter’s tone is markedly different from the imperial letter: where Zeno received praise alongside rebuke, Acacius receives a more searching examination of his role.

The opening reassertion of the inaction criticism — that if Simplicius’s earlier letters had been obeyed, the massacre would not have occurred — is now directed specifically at Acacius. In Letter XIV, the failure was framed as a general breakdown in the chain of execution; here it is Acacius who is told that his failure to press the emperor produced the conditions for violence. The reader should weigh the shift in addressee: the same criticism, delivered to the emperor as a diplomatic rebuke, becomes a pastoral charge when delivered to the patriarch. Simplicius is not accusing Acacius of culpability for the murders but of responsibility for the conditions that permitted them.

The treatment of the ordination is the editorial heart of the letter. Simplicius navigates three positions simultaneously: he acknowledges that the ordination advanced the cause of peace; he notes that it was “not without reproach” and that even the emperor recognizes the precedent must be guarded against; and he explicitly exonerates Acacius from the charge of usurpation. The exoneration is significant because it is also a limitation. By saying that Acacius acted under imperial command and not by his own right, Simplicius strips the ordination of any precedential force for Constantinople’s future claims. Acacius cannot point to this event as evidence that Constantinople has the right to ordain bishops for Antioch, because Simplicius has defined the act as obedience to an imperial command, not an exercise of Constantinopolitan jurisdiction. The exoneration protects Acacius personally while protecting the Nicene order canonically.

The reader should note what this letter adds to the evidence, discussed in the Commentary on Letter XIV, that Canon 28 of Chalcedon was not operative. In Letter XIV, the argument rested on Zeno’s behavior: the emperor framed the ordination as an exception and pledged it would not recur, which he would not have done if Constantinople had an acknowledged right to ordain bishops for other sees. Letter XV sharpens the point from Acacius’s side. Here it is Acacius himself who testifies that he “long held back” from performing the ordination, and who is now seeking to purify the act by formal satisfactio. If Canon 28 were operative — if Constantinople possessed the jurisdictional authority to ordain bishops for the major Eastern sees — then Acacius would have had no reason to hesitate, no reason to frame his compliance as reluctant obedience to an imperial command he “could not refuse,” and no reason to seek satisfaction for having done it. The fact that the patriarch of Constantinople treats his own ordination of an Antiochene bishop as an irregularity requiring formal amends is evidence, from the one party who would have benefited most from invoking Canon 28, that the canon was not in force. All three parties to the exchange — Rome, Constantinople, and the emperor — proceed on the shared assumption that the Nicene order of provincial ordination is the binding norm, and that what happened at Constantinople was a departure requiring justification, not an exercise of established right.

The closing sentence deserves particular attention. Simplicius tells Acacius that since he rightly sees the act as pardonable (because it was commanded), he should give honor to the Fathers by working to ensure no such necessity arises again — especially since Acacius himself is seeking to purify the act by satisfaction. The word satisfactio is a formal canonical term: it means making amends for an irregular act, not merely expressing regret. Acacius has apparently acknowledged the irregularity of the ordination and has offered some form of formal satisfaction to Rome. Simplicius accepts it but turns it into an obligation: if you know it was irregular enough to require satisfaction, then you know it must never be repeated. The forgiveness carries within it the duty of prevention.

The letter has no transmitted dateline in the PL text. The site’s dateline of “the sixteenth day before the Kalends of November (A.D. 478)” appears to have been borrowed from Letter XIII, which carries that date. Since Letter XV responds to the same events as Letter XIV (dated June 22, 479) and references the same imperial and patriarchal correspondence about the Antioch massacre, it belongs to 479 — probably to the summer or autumn of that year, after the exchange of letters between Rome, Constantinople, and the imperial court about the crisis had been completed.