The relationship between ancient religion and ancient politics was not the separation of church and state that modern Western societies have institutionalized but rather a thorough interpenetration in which religious authority and political authority were mutually constitutive.

In the Greek poleis, the gods were the gods of the city: Athena for Athens, Apollo for Delphi, Zeus for Olympia. Religious festivals were civic events; temples were civic buildings; sacrificial ritual was a fundamental act of community formation. The priest was not a separate religious professional standing outside civic life but a civic official performing a civic function. The distinction between the religious and the political that Christianity introduced — which could coexist with or challenge secular authority — did not exist in the same way for pre-Christian antiquity.

Roman religion was similarly civic in structure, with the additional dimension of the Roman state's particular relationship to its gods: the gods had contracted, in some sense, to protect Rome, and Rome's obligations were ritual correctness (the pax deorum, the peace of the gods) rather than moral conformity to divine commands. The Pontifex Maximus — the chief religious official — was a political position; Julius Caesar and Augustus both held it.

The integration of ruler cult into Hellenistic and Roman political religion represents a particular strain of this interpenetration. Alexander was recognized as divine by several Greek cities during his lifetime; Ptolemaic kings and queens were identified with Egyptian gods; Roman emperors received divine honors in the Greek East during their lifetimes and official apotheosis after death. The political function of divine kingship — creating loyalty to a personal ruler rather than to a civic or ethnic community — is clear.