Petilianus was a Donatist bishop of Constantina (Cirta) in Numidia at the end of the fourth and the beginning of the fifth century. He wrote a letter to his clergy, in which he provided  them with arguments against the Catholics. Augustine responded to it gradually, when he was able to obtain copies of Petilianus`s work, and so he wrote the first book of his answer in 400, the second in 401, and the third between 401 and 403.