Whenever someone says something is “interesting”, that means it isn’t.

Mithraism is a pretty interesting religion that they don’t know very much about.  Most of what has been pieced together about it comes from the discovery of temples and artifacts; the Mithraics weren’t too big on the whole “Writing Down Your Holy Book” thing.  Archaelogists have found mithraeums, which would be Temples to Mithras, throughout the Roman world, including a very famous one in the Bank area of London (I used to walk by it almost daily, ah, those were the days….), but other than some vague generalities about the cult, archeologists don’t seem to know much about it.  It was a warrior religion, it was hierarchical, and it was technically monotheistic.  Mithras, the god, is also found in Zoroastrianism, but as a different version of the god that was worshipped by the Romans.  And the major symbolic event in it was the killing of a bull. Can you imagine a world where that symbol would be everywhere instead of crosses?  At the very least, it’s a tad bit more artistically challenging.