Letter V is the first of Simplicius’s many letters to Acacius of Constantinople, and it opens the long correspondence whose continuation, after Simplicius’s death, would produce the Acacian Schism of 484. The moment at which it is written is one of apparent cooperation: Zeno has been restored (August 476), Basiliscus is dead, Acacius had refused communion with Basiliscus’s Encyclical and stood firmly for Chalcedon, and Rome’s confidence in the bishop of Constantinople is high. Simplicius writes to Acacius as a brother and fellow bishop, and commissions him as a kind of legate to press the emperor on Rome’s behalf. The reader should note the historical poignancy: the cooperation Simplicius presupposes would not hold, and Acacius himself would, within a few years, drift into the compromises that produced the Henoticon of 482 and — after Simplicius was gone — the excommunication that began the schism.

The rhetorical strategy of the letter is tight and specific. Timothy Aelurus is pressing for a universal council that would vindicate his status and reopen the Chalcedonian settlement. Simplicius’s task is to prevent that council from being called. Rather than writing to Zeno directly, he writes to Acacius and asks him to carry the petition to the emperor — together with presbyters and monks from the Eastern monasteries — and to present copies of the Leo-to-Leo correspondence as the standard of what the emperor should now do. The structural move is significant: Simplicius deploys Acacius as Rome’s voice at the imperial court, treating him as a cooperating patriarch who will press Rome’s case. The authority is Rome’s; the channel is Acacius.

The theological argument for refusing the synod has two parts. First, Roman doctrine is not to be disputed: the doctrine of Simplicius’s predecessors of holy memory stands, “against which it is impious to dispute.” The Latin nefas is not a mild word — it designates religious-legal violation, sacrilege. To treat argument against Roman doctrine as nefas is to put it outside the category of legitimate theological dispute. This claim is the primacy ground on which the refusal of the synod rests: Rome has spoken, and what Rome has taught cannot be reopened. Second, synods are structurally not for reopening settled matters. Simplicius identifies the precedents — Arius, Nestorius, Dioscorus, Eutyches — as cases where synods were rightly called because something new had arisen requiring conciliar determination. Timothy Aelurus’s position is not new; it is the continuation of a condemned heresy. Therefore no new synod is warranted. The two arguments together close the door to any fresh conciliar action: what Rome has defined cannot be disputed, and no council can be called for the purpose of revisiting it.

A third argument concerns the emperor. Simplicius sends Acacius copies of the Leo-to-Leo correspondence and asks that Zeno “consider as written to himself” whatever was handed down to the princes before him. The argument treats papal correspondence with predecessor emperors as carrying continuing authority across imperial successions: because Zeno is the successor of the Emperor Leo, the letters Pope Leo sent to Emperor Leo are binding on him. This is the continuity argument applied to imperial office — the same kind of continuity argument Simplicius makes about his own office (“the doctrine of Our predecessors”). Papal correspondence does not have a shelf life ending with the death of its original recipient; it binds the office, and therefore binds the successor who holds the office.

The letter closes with a biblical echo worth noticing. Simplicius invokes Proverbs 21:1 — “the king’s heart is in the hand of the Lord” — and presses the point that Zeno must know no other source for his power than God. The allusion is common in late-antique papal correspondence with emperors, but its deployment here has a particular edge: Simplicius is writing to an emperor who had just been displaced and restored, whose political legitimacy was contested, and who was being pressed by heretical voices to hold a council that would undo what his predecessors had ratified. The reminder that his power comes from God alone is also a reminder that his obligation is to God’s order — not to the theological ambitions of those around him. The prayer at the end of the letter — that God would come to the Christians’ aid by holding the king’s heart established in His hand — is the theological counterpart to the practical request: that Acacius press the emperor, and that the emperor refuse the synod.

One final point for the reader. This letter records a moment at which Rome and Constantinople were working together against a common enemy. The moment would not last. The drift that produced the Acacian Schism was already beginning to unfold in the pressures Simplicius describes here — the push for a new synod, the imperial temptation to compromise, the heretical figures maneuvering at court. Within five years, the Emperor Zeno would issue the Henoticon (482), an imperial formula designed to reconcile Monophysites and Chalcedonians that Rome would judge insufficient; within eight years, Felix III would excommunicate Acacius; within a generation, the Acacian Schism would divide the sees of Peter and Constantinople for thirty-five years. Simplicius’s Letter V stands at the beginning of that trajectory, and its tone of trust and cooperation is all the more striking for what was coming. The primacy claims the letter registers — Roman doctrine as undisputable, synods as limited to new questions, papal correspondence as binding successor emperors — are precisely the claims that would be tested in the decades that followed, and that would finally be confirmed, against Eastern resistance, by the Formula of Hormisdas that ended the schism in 519.