Roman religion was a complex weave of cultic threads. The earliest Romans believed in animism, the divine powers residing in nature and the human environment. As time went on they expanded their religious horizons through contact with their Etruscan and South Italian and Sicilian Greek neighbors, whose gods took human forms and personalities. When adopted by the Romans these anthropomorphic Greco-Etruscan deities, with new names like Jupiter, Juno, and Mars, became the Roman pantheon familiar to us today.
By the late 3rd century BC a stream of strange and exotic Oriental and Egyptianizing cults such as that of Cybele, the Anatolian mother goddess, and of the Egyptian Isis and Serapis began to appear in Rome as her political domination of the Mediterranean basin spread. The Romans steadily aded new deities to honor a wide range of abstract social forces such as Dea Roma, the personaification of the spirit of Rome; Concordia, the goddess of "Harmonius Agreement;" and Victoria, the Roman equivalent of the Greek Nike.
With the advent of the Imperial stae in 31 BC the Romans embarked on three centuries of worship of their supreme rulers. The first emperor, Augustus, refused official deification, but, as the adopted son of the already deified Caesar, his divinization was inevitable upon his death. A select group of subsequent emperors and their family members were also given the hhonor of deification.
The monothistic religions of Judaism and Christianity grew in populatiry as the Roman empire expanded, and relations between the Roman state and the Jews or Christians altered with historic and political events. The monotheistic beliefs and seemingly strange religious practices of the Jews, such as keeping the Sabbath holy, circumcision, and dietary restrictions, inevitably collided with official Roman practices. Also, the refusal of Jews and Christians to acccept the notion of the mperor as god created a climate of suspicion. But although at first hte Roman state looked upon early Christians as an underclass of potentially dangerous revolutionaries, eventuallyt he stae officially converted to Christianity under the emperor Constantine (AD 306-337).