Religion in ancient Rome encompassed the religious beliefs and cult practices regarded by the Romans as indigenous and central to their identity as a people, as well as the various and many cults imported from other peoples brought under Roman rule. Romans thus offered cult to innumerable deities who influenced every aspect of both the natural world and human affairs. The establishment of these cults was credited to Rome's divine ancestors, founders, and kings, and to conquered nations and allies. Their temples provided the most visible and sacred manifestations of Rome's history and institutions. Rome's ancient boundary enclosed an intrinsically sacred city.

Participation in traditional religious rituals was a practical and moral necessity for Romans of every class and occupation, and was embedded in personal, domestic and public life. Cult could be offered any deity or any combination of deities, as long as it did not offend the mos maiorum, the "custom of the ancestors," that is, Roman tradition. Piety was the correct application of ritual and divine honours, especially in the form of sacrificial offerings. In return, the gods were likely to benefit their worshipers. Impieties such as religious negligence, superstition and self-indulgence could provoke divine wrath against the State.