During his time as prefect, he put the heretic Priscillian on trial, and found him guilty of practicing magic.
Though Hydatius consistently characterizes Iberian heretics as Manichees, it is generally believed that he meant Priscillianists, followers of the ascetic bishop Priscillian, who had been condemned as a heretic by several church councils and executed as a magician by the emperor Magnus Maximus around 385.