Irenaeus, Saint (Īrĭnēˈəs) [key], c.125–c.202, Greek theologian, bishop of Lyons, and one of the Fathers of the Church. Born in Asia Minor, he was a disciple of St. Polycarp. Irenaeus went to Rome to plead for leniency toward the Montanists (see Montanism) and for those Eastern Christians who were threatened with excommunication because they did not observe the Roman date for Easter. He remained in the West and died in Gaul. Irenaeus was the earliest Father of the Church to systematize those Christian beliefs that would later be accepted as orthodox doctrine and is cited frequently by later theologians. Only two of his works survive—neither in the original Greek. The five-volume Against Heresies establishes Christian doctrine against the Gnostics and incidentally supplies much information on Gnosticism. The Epideixix is a concise exposition of Christian doctrine (tr. by J. P. Smith, Proof of the Apostolic Preaching, 1952). Feast: June 28.