Lucius Caecilius Firmianus signo Lactantius (c. 250 – c. 325) was an early Christian author who became an advisor to Roman emperor Constantine I, guiding his Christian religious policy in its initial stages of emergence, and a tutor to his son Crispus. His most important work is the Institutiones Divinae ("The Divine Institutes"), an apologetic treatise intended to establish the reasonableness and truth of Christianity to pagan critics.
He is best known for his apologetic works, widely read during the Renaissance by humanists, who called Lactantius the "Christian Cicero". Also often attributed to Lactantius is the poem The Phoenix, which is based on the myth of the phoenix from Egypt and Arabia. Though the poem is not clearly Christian in its motifs, modern scholars have found some literary evidence in the text to suggest the author had a Christian interpretation of the eastern myth as a symbol of resurrection.
Lactantius was of Punic or Berber origin, born into a pagan family. He was a pupil of Arnobius who taught at Sicca Veneria, an important city in Numidia (corresponding to today's city of El Kef in Tunisia). In his early life, he taught rhetoric in his native town, which may have been Cirta in Numidia, where an inscription mentions a certain "L. Caecilius Firmianus".
Lactantius had a successful public career at first. At the request of the Roman emperor Diocletian, he became an official professor of rhetoric in Nicomedia; the voyage from Africa is described in his poem Hodoeporicum (now lost). There, he associated in the imperial circle with the administrator and polemicist Sossianus Hierocles and the pagan philosopher Porphyry; he first met Constantine, and Galerius, whom he cast as villain in the persecutions. Having converted to Christianity, he resigned his post before Diocletian's purging of Christians from his immediate staff and before the publication of Diocletian's first "Edict against the Christians" (February 24, 303).