This paper analyses the arguments that Augustine of Hippo gives in the first book of his work Contra epistulam Parmeniani with the aim of justifying Constantine the Great’s measures against the Donatists. Although these arguments are probably preceded in time by similar remarks in the second book of Augustine’s Contra litteras Petiliani, they represent the first organic statement of Augustine’s defense of the emperor’s right to judge about religious matters and to persecute schismatics and heretics. This paper suggests that Augustine never changed his mind about such a right in principle, but only about its practical usefulness for settling religious disputes.
