Roman religion ran on a deal: I give so that you give
Romans credited their empire to piety, but their faith asked little in the way of belief. What mattered was performing prayers and sacrifices correctly under a bargain summed up as do ut des. Priests were elected politicians, Julius Caesar held the top priesthood before becoming consul, and foreign gods were absorbed rather than banned.
Early Rome borrowed freely. Greek settlers in Italy brought practices such as the worship of Apollo, and Romans matched their own gods to Greek ones, reworking the myths and images much as the Etruscans had. The Etruscans also supplied augury, the reading of divine will that the state consulted before acting. Legend traced most institutions to Numa Pompilius, the Sabine second king, said to have bargained with the gods face to face. That inherited religion underpinned the mos maiorum, the ancestral custom at the core of Roman identity.
There was no wall between temple and state. Under the Republic, from 509 to 27 BC, elected magistrates also served as augurs and pontiffs, married and pursued political careers. Even a sceptic like Cicero, himself an augur, valued religion for keeping society orderly. A triumph was at heart a religious parade in which a winning general gave part of his loot to the gods, above all Jupiter, and the Punic Wars of 264 to 146 BC left Rome dotted with temples vowed for victory.
Daily devotion was domestic. Every house had a shrine to its family gods, springs and groves were sacred, and the calendar followed the festivals. Women led certain rites, and the Vestals tended the city's sacred hearth for centuries. As Rome expanded it adopted conquered peoples' deities; Isis, Cybele, Mithras and Sol Invictus reached as far as Britain. Secretive mystery cults still worried conservatives, and the Senate moved to restrict the Bacchanals in 186 BC. Judaism's insistence on one God produced exemptions but also conflict, and religious disputes helped spark both the First Jewish-Roman War and, later, the Bar Kokhba uprising.
Augustus dressed up one-man rule with a sweeping religious revival, redirecting public vows toward the emperor's welfare. The Imperial cult became a badge of loyalty across the provinces, so refusing it looked like treason. Romans saw Christianity as atheism or a new superstition, yet in 380 it became the official state religion.
Source: Religion in ancient Rome
