The correspondence of Augustine can be studied in order to obtain an accurate portrait of the social composition of the Donatist Church, especially in Hippo Regius where, at the time he arrived there, the Catholic community was poor and barely subsisting. From then, Augustine began his correspondence with the Donatists with some letters addressed to Donatist laymen in 395 and, at the same time, he wrote to the Donatist bishops proposing them a debate centred on theological matters only.
The purpose of this paper is to explain how, until the conference of Carthage in 411, Augustine granted great importance to the letters as a direct and quick manner to focus his communication and debate with Donatists. He wisely used the letter to address both the Donatist plebs and the aristocrats and the schismatic bishops. In his letters, Augustine displayed a very detailed sort of arguments (historical, scriptural, theological, etc.) to achieve that followers of Donatism apostate from their schismatic faith. In fact, Augustine anticipated in his letters the arguments that he will develop largely in his treaties.
After the Conference of Carthage in 411, a new shift in Augustinian epistolary strategy arose. Besides interrupting his correspondence with the Donatist bishops –now legally heretics– he will address no further letter to the Donatists people with the only exception of the synodal letter 141 –read in 412 by Augustine on behalf of the Council of Zerta–. From then on, Augustine did not use the epistolar format for the debate anymore, and he only used it in order to announce the verdict of condemnation of Donatism by Flavius Marcellinus.