The Romans would allow religious freedom in the conquered territories unless it challenged their rule, they were more interested in the extraction of wealth (Taxes) resources (minerals and goods) and manpower in the form of slaves and recruits for the army.
Christianity was seen as a challenge to their power- Christ as king and a kingdom of heaven, it also challenged their religious,social, cultural and political mores.When the Emperor Constantine converted to Christianity he decreed it the official religion of the empire and pagan gods where displaced through out the empire including Egypt.Then after 600AD the Muslims conquered much of the former Roman empire in the middle east and Islam replaced Christianity. ISIS(Islamic State in Iraq and Syria a terrorist organization) or now IS wants to wipe out all other religions and make feudal Sunni Islam the religion of the world.
The Roman gods were copied from the Greeks almost exclusively.
I often wonder about completely isolated populations that do come up with very similar religious tenants
No conversation about the Egyptian goddess Isis can be complete without discussing Osiris and Horus.
That is a conversation for another thread and only the very curious or history geeks would read it, but that's alright.