Dionysius Exiguus (sixth century) contributed to making Greek patristic literature available in Latin. He was also the creator of the Dionysian Era (Common Era), which we still use today. His Collectio Dionysiana became a basic collection of canonical ius in the Western church during the first millennium. The Collectio Dionysiana was composed of two books: the Liber canonum, and the Liber decretalium. The Liber canonum is a collection of disciplinary decrees from church councils: mostly Eastern, but with some Western (Latin) councils. The Liber decretalium is a collection of decretal letters by the bishops of Rome (plus one imperial statute). The Collectio Dionysiana originated at a time of internal conflicts in the Church of Rome, when various factions used forgeries to claim legitimacy. The Collectio Dionysiana may have been a reaction against the use of forgeries. Dionysius attempted to make the “authentic” sources of church discipline available. The Collectio Dionysiana was later augmented in the form of the Collectio Dionysiana-Hadriana under Pope Hadrian I (eighth century) and sent to Charlemagne. This became the standard collection of canons and decretals for the Frankish Empire.

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.