So, then, after many controversies among them, which are not worthy of mention, a Synod was assembled at Saragossa, at which even the Aquitanian bishops were present. But the heretics did not venture to submit themselves to the judgment of the council; sentence, however, was passed against them in their absence, and Instantius and Salvianus, bishops, with Helpidius and Priscillian, laymen, were condemned. It was also added that if any one should admit the condemned persons to communion, he should understand that the same sentence would be pronounced against himself.
And the duty was entrusted to Ithacius, bishop of Sossuba, of seeing that the decree of the bishops was brought to the knowledge of all, and that Hyginus especially should be excluded from communion, who, though he had been the first to commence open proceedings against the heretics, had afterwards fallen away shamefully and admitted them to communion. In the meantime, Instantius and Salvianus, having been condemned by the judgment of the priests, appoint as bishop in the town of Arles, Priscillian, a layman indeed, but the leader in all these troubles, and who had been condemned along with themselves in the Synod at Saragossa.
This they did with the view of adding to their strength, doubtless imagining that, if they armed with sacerdotal authority a man of bold and subtle character, they would find themselves in a safer position. But then Ydacius and Ithacius pressed forward their measures more ardently, in the belief that the mischief might be suppressed at its beginning. With unwise counsels, however, they applied to secular judges, that by their decrees and prosecutions the heretics might be expelled from the cities.
Accordingly, after many disgraceful squabbles, a rescript was, on the entreaty of Ydacius, obtained from Gratianus, who was then emperor, in virtue of which all heretics were enjoined not only to leave churches or cities, but to be driven forth beyond all the territory under his jurisdiction. When this edict became known, the Gnostics, distrusting their own affairs, did not venture to oppose the judgment, but those of them who bore the name of bishops gave way of their own accord, while fear scattered the rest.
Source: Sacred History (New Advent)