Julius Firmicus Maternus

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Julius Firmicus Maternus was a Roman writer of the fourth century, a Sicilian of senatorial standing, known for two books that point in opposite directions. The first, the Mathesis, is the fullest treatise on astrology to survive from the ancient world; the second, De errore profanarum religionum, is a Christian attack on the very kind of religion the astrologer’s art had served. Most scholars hold that one man wrote both.

The Mathesis — the Greek word means “learning,” and came to stand for the mathematical science of the stars — runs to eight books and was composed in the 330s, dedicated to a Roman official named Lollianus Mavortius. It is a working handbook rather than a defence: it sets out the doctrine of the houses, the aspects of the planets, the influence of the fixed stars, and long catalogues of the fortunes a given configuration was held to bring. Firmicus writes as a man fully inside the discipline. He opens with a defence of the astrologer’s calling and an insistence that the practitioner live a clean and honest life, since one who reads the will of heaven must be worthy of the reading. The work preserves a great deal of older Greek astrological material that would otherwise be lost, and for that reason it remains one of the principal sources for how the art was actually practised under the Roman Empire.

The second book belongs to a changed world. Addressed to the emperors Constantius II and Constans, the sons of Constantine, De errore profanarum religionum argues that the old cults are demonic error and presses the Christian rulers to suppress them by force — even citing scripture to that end. The contrast with the Mathesis is stark enough that earlier readers doubted the two could be the same author; the prevailing scholarly view now accepts the identification, and reads the change as a conversion, the common arc of a Roman of his class in the decades after Constantine. Whether Firmicus saw any tension between casting horoscopes and condemning pagan worship is not something the texts resolve. Astrology and the imperial cult were not the same thing, and a convert might keep the one while renouncing the other.

The two works together make Firmicus a useful witness to a hinge moment. He stands at the point where a thousand years of Greco-Roman star-lore was being written down in its most complete Latin form, and where the empire’s official religion was turning against the gods that lore had assumed. The astrological treatise was copied and consulted through the Middle Ages and the Renaissance, when it became one of the standard authorities for European practitioners; the polemic survives in a single damaged manuscript. Both came down under the same name, and the awkwardness of that pairing is part of what makes him remembered.

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