Saint Bretannio (also Bretanion, Bretannion, Vetranio, Vetranion) was a bishop of Tomi (today Constanţa, Romania) during the fourth century.
[1] According to Sozomen, during the campaign against the Goths in this region, the emperor Valens stopped at Tomi and urged the populace to convert to Arianism and reject the Nicene Creed.
[3] Basil the Great requested of the ruler of Scythia Minor, Junius Soranus (Saran), that he should send him the relics of saints of that region.
The sending of Sabbas' relics and the writing of the actual letter has been attributed to Bretannio.
[3] Baronio, in compiling his martyrology, seems to have arbitrarily assigned him the feast day of January 25.