FIRMICUS, MATERNUS JULIUS, a Latin writer, who lived in the reign of Constantine. His De erroribus pro f anarum religionum, written c. 346 and still extant, attacks the false objects of worship among the Oriental cults and discusses a number of formulae and rites connected with the mysteries. Its declamatory tone contrasts with his eight books on astronomy (Libri VIII. Matheseos) written c. 336.