The people of the late ancient Mediterranean world thought about and encountered gods, angels, demons, heroes, and other spirits on a regular basis. These figures were diverse, ambiguous, and unclassified and were not ascribed any clear or stable moral valence. Whether or not they were helpful or harmful under specific circumstances determined if and what virtues were attributed to them. That all changed in the third century C.E., when a handful of Platonist philosophers--Plotinus, Origen, Porphyry, and Iamblichus--began to produce competing systematic discourses that ordered the realm of...