AnswerWe tend to think of paganism as a monolithic religion, more or less like
Christianity. In fact, the beliefs held in the
Roman Empire were much more diverse and complex than often imagined.
The Romans themselves worshipped gods that were either derived from the Greek and Etruscan pantheons, or were syncretistic derivations of one or both of those pantheons. The principal Roman gods lived on Capitol Hill. However, the Romans also maintained elements of animism, particularly among the Latins of the surrounding rural areas.
The Greeks continued to worship their own gods, who were somewhat different from their Roman counterparts. The principal Greek gods lived on mount Olympus and had somewhat different backgrounds and characteristics to their Roman counterparts.
Many of the elite, especially in Greece, had abandoned formal religions and pursued philosophical thinking about our origins. This sometimes could lead away from philosophy into new religions that seemed allied to the fashionable philosophical thinking of the day.
New cults had sprung up. The ancient Roman sun god, Sol, had largely been supplanted by Mithras, who was for some time a serious competitor to Christ for the devotion of those who sought new religious experiences. By the time of Constantine, Mithras had to some extent been replaced by a new sun god, Sol Invictus, although each was known to be really the same as the other two.
There was also a trend to worship of Egyptian gods, or a syncretism of Egyptian gods and their Greek counterparts. Other religions of the Common Era included the 'mystery religions' which did not divulge all their mysteries to mere novices.
Judaism was well respected and, in spite of two Jewish Wars and several uprisings both in Palestine and in the diaspora, faced no real persecution until the time of Constantine and his Christian successors.
Finally, of course, there was Christianity. Some scholars believe this may have constituted ten per cent of the population of the empire, but concentrated in the east, excluding most of Egypt, and in Africa and Rome itself.