You learn about that when you learn about them. There wasn't one overlaying religion then, and there isn't one now.
Probably the ancient Egyptian religion.
They were true to the ancient people who knew them as a religion.
Polyhtesim
they had their own religion. i guess you could call it ancient egyptian. most people just call their polytheistic religion by their gods names, or say "the egyptian gods"
religion in ancient civilization could be accurate but if there was a way to find out more people would have tried a long time ago.
they studied Christianity after they were conquered
Their religion was what we call the Greek myths., Today, it would probably be referred to as "Paganism".
They practiced the ancient Egyptian religion.
HINDUISM - The World's Ancient RELIGION.
Daoism
The Greek myths were the ancient Greek's religion.
The religion of ancient Rome was Roman religion.