Περὶ Θεοῦ Μοναρχίας. The word μοναρχία, as used by Plato (Polit. 291 C), Aristotle (Polit. III. xiv. 11. εἶδος μοναρχίας βασιλικῆς), Philo Judæus (de Circumcisione, § 2; de Monarchia, Titul.), means “sole government.” Compare Tertullian (adv. Praxean. c. iii.): “If I have gained any knowledge of either language, I am sure that Μοναρχία has no other meaning than ‘single and individual rule.’” Athanasius (de Decretis Nicænæ Synodi, § 26) has preserved part of an Epistle of Dionysius, Bishop of Rome (259–269, a.d.), against the Sabellians: “It will be natural for me now to speak against those who divide, and cut into pieces, and destroy that most sacred doctrine of the Church of God, the Monarchia, making it, as it were, three powers and divided hypostases, and three Godheads;” (ibid.): “It is the doctrine of the presumptuous Marcion to sever and divide the Monarchia into three origins (ἀρχάς).” We see here the sense which Μοναρχία had acquired in Christian Theology: it meant the “Unity of God,” as the one principle and origin of all things. “By the Monarchy is meant the doctrine that the Second and Third Persons in the Ever-blessed Trinity are ever to be referred in our thoughts to the First, as the Fountain of Godhead” (Newman, Athanas. de Decretis Nic. Syn. § 26, note h). Justin Martyr (Euseb. H.E. IV. 18), and Irenæus (ibid. V. 20), had each written a treatise περὶ Μοναρχίας. On the history of Monarchianism see, in this Series, Athanasius, Prolegomena, p. xxiii. sqq.