Hilarius Diaconus a deacon of the Church of Rome in the 4th century, who was sent by pope Liberius, with Lucifer of Cagliari and others, to plead the cause of the orthodox faith before Constantius at the Council of Milan. His boldness was so offensive that he was scourged and banished by order of the emperor. He afterwards supported the violent opinion of Lucifer (q.v.) that, all Arians and heretics must be rebaptized upon applying to be restored to communion in the Church. Two treatises, of doubtful authenticity, are ascribed to him: (1.) Comm. in Epist. Pauli (published often with the works of Ambrose); (2.) Quaest. in Vet. et Nov. Test., published with the works of Augustine (Benedictine edit. 3, App.). The Benedictine editors of St. Ambrose inform us that the manuscripts of the "Commentary" on St. Paul's Epistles differ considerably, and that in some parts there appear t6 be interpolations of long passages. This commentary is said by Dupin to be "clear, plain, and literal, and to give the meaning of the text of St. Paul well enough; but it gives very different explanations from St. Augustine in those places which concern predestination, provocation, grace, and free will." — Lardner, Works, 4, 382; Mosheim, Ch. Hist. cent. 4, pt. 2, ch. 2, n. 43; Dupin, Eccles. Writ. cent. 4; English Cyclopedia.