The Ecclesiastical History of Socrates Scholasticus

Those convened at Sardica, as well as those who had formed a separate council at Philippopolis in Thrace, having severally performed what they deemed requisite, returned to their respective cities. From that time, therefore, the Western church was severed from the Eastern; and the boundary of communion between them was the mountain called Soucis, which divides the Illyrians from the Thracians. As far as this mountain there was indiscriminate communion, although there was a difference of faith; but beyond it they did not commune with one another. Such was the perturbed condition of the churches at that period. Soon after these transactions, the emperor of the Western parts informed his brother Constantius of what had taken place at Sardica, and begged him to restore Paul and Athanasius to their sees. But as Constantius delayed to carry this matter into effect, the emperor of the West again wrote to him, giving him the choice either of re-establishing Paul and Athanasius in their former dignity, and restoring their churches to them; or, on his failing to do this, of regarding him as his enemy, and immediately expecting war. The letter which he addressed to his brother was as follows:

‘Athanasius and Paul are here with me; and I am quite satisfied after investigation, that they are persecuted for the sake of piety. If, therefore, you will pledge yourself to reinstate them in their sees, and to punish those who have so unjustly injured them, I will send them to you; but should you refuse to do this, be assured, that I will myself come thither, and restore them to their own sees, in spite of your opposition.’