5 Having therefore laid aside that question as one on which there was a doubt, I asked how they could justify their separation of themselves from all other Christians who had done them no wrong, who throughout the world preserved the order of succession, and were established in the most ancient churches, but had no knowledge whatever as to who were traditors in Africa; and who assuredly could not hold communion with others than those whom they had heard of as occupying the episcopal sees. He answered that the foreign churches had done them no wrong, up to the time when they had consented to the death of those who, as he had said, had suffered in the Macarian persecution. Here I might have said that it was impossible for the innocence of the foreign churches to be affected by the offense given in the time of Macarius, seeing that it could not be proved that he had done with their sanction what he did. I preferred, however, to save time by asking whether, supposing that the foreign churches had, through the cruelties of Macarius, lost their innocence from the time in which they were said to have approved of these, it could even be proved that up to that time the Donatists had remained in unity with the Eastern churches and other parts of the world.
6. Thereupon he produced a certain volume, by which he wished to show that a Council at Sardica had sent a letter to African bishops who belonged to the party of Donatus. When this was read aloud, I heard the name Donatus among the bishops to whom the writing had been sent. I therefore insisted upon being told whether this was the Donatus from whom their faction takes its name; as it was possible that they had written to some bishop named Donatus belonging to another section [heresy], especially since in these names no mention had been made of Africa. How then, I asked, could it be proved that we must believe the Donatus here named to be the Donatist bishop, when it could not even be proved that this letter had been specially directed to bishops in Africa? For although Donatus is a common African name, there is nothing improbable in the supposition, that either some one in other countries should be found bearing an African name, or that a native of Africa should be made a bishop there. We found, moreover, no day or name of consul given in the letter, from which any certain light might have been furnished by comparison of dates. I had indeed once heard that the Arians, when they had separated from the Catholic communion, had endeavoured to ally the Donatists in Africa with themselves; and my brother Alypius recalled this to me at the time in a whisper. Having then taken up the volume itself, and glancing over the decrees of the said Council, I read that Athanasius, Catholic bishop of Alexandria, who was so conspicuous as a debater in the keen controversies with the Arians, and Julius, bishop of the Roman Church, also a Catholic, had been condemned by that Council of Sardica; from which we were sure that it was a Council of Arians, against which heretics these Catholic bishops had contended with singular fervour. I therefore wished to take up and carry with me the volume, in order to give more pains to find out the date of the Council. He refused it, however, saying that I could get it there if I wished to study anything in it. I asked also that he would allow me to mark the volume; for I feared, I confess, lest, if perchance necessity arose for my asking to consult it, another should be substituted in its room. This also he refused.
Source: Letters (New Advent)