Hurter distinguishes these three documents thus: (1) epistola, the private letter of Turribius to Leo; (2) commonitorium, the detailed statement (under 16 heads) of the Priscillianist errors; and (3) libellus, Turribius’ refutation of each head. This heresy was of Spanish origin, having been broached by Priscillian about 380. Their views will be seen in the sequel.