“Ignatius (d. 110) engaged both pagans and heretical Christians, particularly docetists, with the gospel…”

“Employing the language of Greek philosophy, Justin [Martyr, d. 165] communicated through public debates and written treatises, directing his message to Jews, pagan intellectuals, and Christian heretics…”

“While serving as bishop of Alexandria for forty-five years, Athanasius [c. 296–373] also evangelized heretics, particularly as he defended the church against Arian teaching…”

“Augustine [354–430] also served as a missionary of sorts to heretics, defending the church against Manichean, Donatist, and Pelagian teaching…”

“[Irish monk] Columban [c. 543–615] proclaimed the gospel to heretics, particularly the Arian Lombards in Italy.”

– Edward L. Smither, Christian Mission: A Concise Global History