There follow the times of our own day, both difficult and dangerous. In these the churches have been defiled with no ordinary evil, and all things thrown into confusion. For then, for the first time, the infamous heresy of the Gnostics was detected in Spain— a deadly superstition which concealed itself under mystic rites. The birthplace of that mischief was the East, and specially Egypt, but from what beginnings it there sprang up and increased is not easy to explain. Marcus was the first to introduce it into Spain, having set out from Egypt, his birthplace being Memphis.
His pupils were a certain Agape, a woman of no mean origin, and a rhetorician named Helpidius. By these again Priscillian was instructed, a man of noble birth, of great riches, bold, restless, eloquent, learned through much reading, very ready at debate and discussion— in fact, altogether a happy man, if he had not ruined an excellent intellect by wicked studies. Undoubtedly, there were to be seen in him many admirable qualities both of mind and body. He was able to spend much time in watchfulness, and to endure both hunger and thirst; he had little desire for amassing wealth, and he was most economical in the use of it.
But at the same time he was a very vain man, and was much more puffed up than he ought to have been with the knowledge of mere earthly things: moreover, it was believed that he had practised magical arts from his boyhood. He, after having himself adopted the pernicious system referred to, drew into its acceptance many persons of noble rank and multitudes of the common people by the arts of persuasion and flattery which he possessed. Besides this, women who were fond of novelties and of unstable faith, as well as of a prurient curiosity in all things, flocked to him in crowds.
It increased this tendency that he exhibited, a kind of humility in his countenance and manner, and thus excited in all a greater honor and respect for himself. And now by degrees the wasting disorder of that heresy had pervaded the most of Spain, and even some of the bishops came under its depraving influence. Among these, Instantius and Salvianus had taken up the cause of Priscillian, not only by expressing their concurrence in his views, but even by binding themselves to him with a kind of oath.
This went on until Hyginus, bishop of Cordova, who dwelt in the vicinity, found out how matters stood, and reported the whole to Ydacius, priest of Emerita. But he, by harassing Instantius and his confederates without measure, and beyond what the occasion called for, applied, as it were, a torch to the growing conflagration, so that he rather exasperated than suppressed these evil men.
Source: Sacred History (New Advent)