The term Μοναρχία first acquired importance in patristic literature in Justin’s work De monarchia, against Polytheism.  Of the lost letter of Irenæus to the Roman Presbyter Florinus, who was deposed for heresy, presumably gnostic, the title, according to Eusebius (H.E. v. 20), was περὶ Μοναρχίας, ἢ περὶ τοῦ μὴ εἶναι τὸν θεὸν ποιητὴν κακῶν.  Later it came to be used to express not the Divine unity as opposed to Polytheism or Oriental Dualism, but the Divine unity as opposed to Tritheism.  Vide the words of Dionysius of Rome, as quoted by Athan. De Decretis, § 26, “Next let me turn to those who cut in pieces, divide, and destroy that most sacred doctrine of the church of God, the divine Monarchy, making it, as it were, three powers and divided subsistences and three godheads.”  So St. Basil Cont. Eunom. ii. ᾽Αρχὴ μὲν οὖν πατρὸς οὐδεμία, ἀρχὴ δὲ τοῦ υἱοῦ ὁ πατήρ.  And in Ep. xxxviii. ᾽Αλλά τίς ἐστι δύναμις ἀγεννήτως καὶ ἀνάρχως ὑφεοτῶσα ἥτις ἐςτὶν αἰτία τῆς ἁπάντων τῶν ὄντων αἰτίας, ἐκ γὰρ τοῦ πατρὸς ὁ υἱ& 232·ς δι᾽ οὗ τὰ πάντα.  And in Ep. cxxv. Ενα γὰρ οἴδαμεν ἀγέννητον καὶ μίαν τῶν πάντων ἀρχὴν, τὸν πατέρα τοῦ κυρίου ἡμῶν ᾽Ιησοῦ Χριστοῦ.  On the doctrine and its exponents compare § 72 of the De Sp. S. On the other hand “Monarchians” was a name connoting heresy when applied to those who pushed the doctrine of the Unity to an extreme, involving denial of a Trinity.  Of these, among the more noteworthy were Paul of Samosata, bp. of Antioch, who was deposed in 269, a representative of thinkers who have been called dynamical monarchians, and Praxeas (supposed by some to be a nickname), who taught at Rome in the reign of Marcus Aurelius, and of whom Tertullian, the originator of the term patripassians, as applied to Monarchians, wrote “Paracletum fugavit et patrem crucifixit.”  This heretical Monarchianism culminated in Sabellius, the “most original, ingenious, and profound of the Monarchians.”  Schaff. Hist. Chr. Church, i. 293.  cf. Gisseler, i. p. 127, Harnack’s Monarchianismus in Herzog’s Real Encyclopædie, Vol. x.  Thomasius Dog. Gesch. i. p. 179, and Fialon Et. Hist. p. 241.