St. Irenaeus was born at Smyrna in Asia Minor, where he studied under St. Polycarp, the disciple of St. John the Beloved.

After living at Rome for a time, he settled in Lyons in 177, where he was consecrated as bishop of a Greek-speaking community. He mastered the Greek and Latin languages, and served in France and Rome against the Gnostic movement.

His most famous work, Against the Heresies, describes and refutes the teachings of the Gnostics, while explaining about the gospels, the sacraments, apostolic tradition, and the hierarchy of the church.