Faustinus a priest of the sect of the Luciferians (q.v.) in the fourth century. He shared in the persecution they experienced, but was set free by the intervention of the emperor Theodosius, to whom be presented a petition praying for protection to be extended to himself and others who associated with him; this the emperor granted, and Damasus's papal persecutions were stayed. He wrote a treatise, De Trinitate sive de Fide contra Arianes (Concerning the Faith, against the Arians). The discourse is dedicated to the empress Flacilla, and divided into seven chapters. He begins by stating the heresies of the Arians, and then combats them from Scripture. In chap. ii he proves that the word Son belongs to our Saviour, but leaves untouched the question whether the word applies to him as God or man, taking for granted the former; in chap. 3 he shows the omnipotence and perpetual endurance of Christ; explains in chap. iv Joh 14:28; in chap. 5, the qualifications implied in Ac 2:36 are pointed out as belonging only to God; and chap. 7 is a short dissertation on the Holy Spirit. He wrote also Fides Theodosio imp. oblata (according to Mabillon, about A.D. 380):- Libellus Precum, a petition addressed to the emperors Valentinian and Theodosius, relating and requesting to be freed from the persecutions which he, Marcellinus, and others were suffering in consequence of being Luciferians. A short account of this sect is prefixed by Faustinus to the petition. His remains will be found in Galland, Bib. Max. Patr. 7:441, and in Migne, Patrol. Curses, 13:38 sq.-Clarke, Success. Sac. Lit.; Lardner, Works, 4:250.