Hailing from North Africa, Lactantius was an imperial professor of Latin rhetoric, a position that brought him to the courts of the emperors Diocletian and Constantine. This chapter explores themes in his Divine Institutes that bear on his legal thought. In addition to setting out Lactantius’s conception of religious tolerance and its influence on the emperor Constantine’s religious policy, the chapter considers the role of “divine law” in Lactantius’s work. He found the first two principles of divine law in Matt 22:36–40 and considered them equivalent to pietas and aequitas in Cicero’s thought. Just as Roman citizens were defined by their access to Roman law, so adherence to divine law, for Lactantius, constituted both Christian and Roman identity. After Augustine of Hippo rejected Lactantius’s suggestion that the law of the state could be a faithful image of the divine law, Western medieval scholars largely ignored the legal thrust of Lactantius’s arguments. Nevertheless, his advocacy of religious tolerance gained currency in recent times, when the Second Vatican Council embraced it.

Ambrosiaster, an early Christian exegete writing in Latin at the end of the fourth century in Rome, was a thinker whose mind was profoundly shaped by notions of law. He devoted considerable attention to questions of the relation between various kinds of law: the law of nature (lex naturalis), the Mosaic Law, Roman law, and Christian law (“the law of faith”). As an interpreter of the Pauline corpus, he was especially influenced by Paul’s discussion of law in the Epistle to the Romans, where the Apostle argued, “When Gentiles who have not the law do by nature what the law requires, they are a law to themselves” (Rom 2:14). Ambrosiaster saw contemporary Roman law as derived partly from natural law, partly from Mosaic law, and partly from the Greeks. As a result, he did not hesitate to justify both Christian doctrine and Christian practice by referring to Roman legal traditions. Because Ambrosiaster’s Pauline commentary was transmitted in the Middle Ages under the name of Ambrose, and because his Questions on the Old and New Testaments was ascribed to Augustine, he exerted great influence on the subsequent tradition, especially on medieval canon law.