Letter XLII is the shortest letter in the present batch, and at first glance the most mundane: a warning about a fraud posing as Leo’s deacon in Gaul. But the disciplinary mechanism Leo employs here is worth noting precisely because it appears in such a routine context.

Leo directs Ravennius to have Petronianus “expelled from the communion of all churches” — not from the diocese of Arles, not from Ravennius’s own jurisdiction, but from the communion of all churches in the province. This is Leo using the Roman see’s communion authority as the instrument of discipline across an entire ecclesiastical province. Ravennius is to alert all the provincial bishops and coordinate a province-wide exclusion. The direction comes from Rome; its execution is Ravennius’s responsibility; its scope is the entire province.

The fraud itself is telling: Petronianus claims to be Leo’s deacon. The prestige that makes such a claim plausible is the prestige of the Roman see. Petronianus does not claim to be the deacon of any Eastern patriarch or Gallic metropolitan; he claims the one title that would open doors across the length of Gaul — a representative of the Roman bishop. The impersonation is, in its perverse way, a testimony to what the authority of the Apostolic See commanded in the province.

The letter is dated August 26, 449 — four days after the Arles election confirmation letters and the same week that news of the Latrocinium may have been beginning to reach Rome. Leo’s response to Ephesus II will fill the next several letters; but before it does, he closes this Gallic cluster with a characteristic act of discipline: clear, decisive, and directed with the authority of the Apostolic See.