Julius Firmicus Maternus, a Latin writer and notable astrologer, who lived in the reign of Constantine and his successors.

About the year 346 he composed a work entitled De erroribus profanarum religionum, which he inscribed to Constantius and Constans, the sons of Constantine, and which is still extant. In the first part (chs. 1‑17) he attacks the false objects of worship among the Oriental cults; in the second (chs. 18‑29) he discusses a number of formulae and rites connected with the mysteries. The whole tone of the work is fanatical and declamatory rather than argumentative, and is thus in such sharp contrast with the eight books on astronomy/astrology (Libri VIII Matheseos) bearing the same author's name, that the two works have usually been attributed to different writers. Mommsen (Hermes vol. 29, pp. 468‑472) has, however, shown that the astronomy — a work interfused with an urbane Neoplatonic spirit — was composed about 336 and not in 354 as was formerly held. When we add to this the similarity of style, and the fact that each betrays a connection with Sicily, there is the strongest reason for claiming the same author for the two books, though it shows that in the 4th century acceptance of Christianity did not always mean an advance in ethical standpoint.

The Christian work is preserved in a Palatine manuscript in the Vatican library. It was first printed at Strassburg in 1562, and has been reprinted several times, both separately and along with the writings of Minucius Felix, Cyprian or Arnobius. The most correct editions are those by Conr. Bursian (Leipzig, 1856), and by C Halm, in his Minucius Felix (Corp. Scr. Eccl, Lat. ii.), (Vienna, 1867). The Neoplatonist work was first printed by Aldus Manutius in 1501, and has often been reprinted. For full discussions see G Ebert, Gesch. der chr. let. Litt., ed. 1889; p. 129 ff.; O Bardenhewer, Patrologie, ed. 1901, p. 354.