a. =Irenæus=, a pupil of Polycarp, was a native of Asia Minor. According to the _Vita Polycarpi_ of Pionius he lived in Rome at the time of Polycarp’s death as a teacher, and it is not improbable that he had gone there in company with his master (§ 37, 2). Subsequently he settled in Gaul, and held the office of presbyter at Lyons. During his absence at Rome as the bearer of a tract by the imprisoned confessors of Lyons on the Montanist controversy to the Roman bishop Eleutherus, Pothinus, the aged bishop of Lyons, fell a victim to the dreadful persecution of Marcus Aurelius which raged in Gaul. Irenæus succeeded him as bishop in A.D. 178. About the time and manner of his death nothing certain is known. Jerome, indeed, once quite casually designates him a martyr, but since none of the earlier Church Fathers, who speak of him, know anything of this, it cannot be maintained with any confidence. Gentleness and moderation, combined with earnestness and decision, as well as the most lively interest in the catholicity of the church and the purity of its doctrine according to scripture and tradition, were the qualities that make him the most important and trustworthy witness to his own age, and led to his being recognised in all times as one of the ablest and most influential teachers of the church and a most successful opponent of heretical Gnosticism. His chief work against the Gnostics: Ἔλεγχος καὶ ἀνατροπὴ τῆς ψευδονύμου γνώσεως (_Adv. hæreses_) in 5 books, is mainly an _ex professo_ directed against the Valentinians and the schools of Ptolemy and Marcus There is appended to it, beyond what had been proposed at the beginning, a short discussion of the views of other Gnostics, the basis of which may be found in an older treatise, perhaps in the Syntagma of Justin. The last four books give the express scripture proofs to sustain the general confutation, without doing this, however, in a complete manner; at the same time there is rapid movement amid many digressions and excursuses. This work has come down to us in a complete form only in an old translation literally rendered in barbarous Latin, even to the reproduction of misunderstood words, which was used as early as by Tertullian in his treatise against the Valentinians. We are indebted to the writings of the heresiologists Hippolytus and Epiphanius for the preservation of many remarkable fragments of the original, with or without the author’s name. Of his other writings we have only a few faint reminiscences. Two epistles addressed to the Roman presbyter Florinus combat the Valentinian heresy to which Florinus was inclined. During the