LUCIUS CELIUS FIRMIANUS, was, according to the common account, born at Firmium in Italy about the middle of the third century. After he had studied at Sicca Veneræ in Africa, under Ammionius the celebrated teacher of rhetoric, at the request of Diocletian he settled, about A.D. 301, at Nicomedia, in Bithynia, and there opened a school for Latin eloquence. Being, however, unsuccessful as a teacher, he abandoned his favourite study of rhetoric, and became author by profession. His conversion to Christianity about this period was probably the chief cause of the extreme poverty under which he struggled, even after the accession of Constantine, when he was summoned to Gaul to act as tutor to Crispus, the eldest son of the Emperor. Lactantius died at Treves about A.D. 325.

The theological works of Lactantius, still extant, are,—Divinærum Institutionum libri vii., containing an exposure of the error and absurdity of pagan idolatry and philosophy, and a vindication of the truth and purity of Christianity; De Ira Dei, written against the Epicureans in support of the doctrine of rewards and punishments; De Officio Dei; and De Mortibus Persecutorum.

As a Latin prose-writer, Lactantius is second only to the writers of the Augustan age; and of all who have imitated the graceful and energetic eloquence of Cicero he has been the most successful. In theology he is more rhetorical than logical, fonder of the dogmas of heathen philosophy than of the doctrines of the gospel, and therefore very unsafe as a teacher of Christianity.