Letter XCVI is one of the shortest letters in the corpus, but it is not a slight document. Its brevity is the brevity of a directive that does not need elaboration: Leo tells Ravennium what date Easter is to be kept, names the theological basis, and instructs him to communicate it throughout the province. The letter is complete in one short paragraph.

What makes XCVI significant for the primacy question is the clause that grounds the directive: “divine institution and paternal tradition have willed this to belong to Our solicitude.” The sollicitudo formula — present throughout the Illyrian correspondence of the early 440s, operative in Leo’s dealings with the Gallic churches in Letter X, and recurring across the pre-Chalcedon letters — appears here in a direct and unambiguous form. The designation of the Paschal date is a function of the Roman bishop’s universal pastoral responsibility, and that responsibility is grounded not in convention or collegial agreement but in divine institution and paternal tradition alike. Leo is not consulting Ravennium; he is instructing him. The province of Arles is to celebrate Easter on March 23 because Rome has designated March 23.

The letter also illustrates the range of the sollicitudo concept. In the Illyrian and Gallic correspondence, it grounds Leo’s appellate jurisdiction and his authority to install and instruct vicariates. Here it grounds something that might appear purely liturgical — the date of the central Christian feast. But for Leo, the two are continuous: the Roman bishop’s solicitude for all the Churches extends to every dimension of their common life, and unity in the celebration of the Lord’s Pascha is not separable from unity in the faith itself. A Church that keeps a different Easter is a Church that is, in some sense, maintaining a different devotion — and that deviation, however technical it might seem, falls within the scope of what the Roman bishop’s office is charged to prevent.