Multicultural Rome.

By the first century C.E., Rome had a population of nearly a million people. It was huge by the standards even of the early modern world: in seventeenth-century Europe, only London, Paris, and Constantinople had populations above 400,000. It was also a magnet for immigrants from the empire, which by the mid-century stretched from Britain to the Middle East. Many came as slaves, who were then freed and as freedmen became Roman citizens. They brought their religious beliefs with them.

Magic.

Along with the new cults there was an up-surge of interest in magic and astrology. The attraction of magic was that it purported to give mortals some control over life and death and the powers of the Underworld. The magician, with his handbooks of magic spells, gave...