Was mithraism the first universal religion?
Greek and Roman Polytheism were probably the first universal religions since they tended to synchretize easily with local and foreign pantheons whenever their culture took over other peoples. Other cultures did the same but not to such great lengths as the Graeco-Roman world. Mithraism as a religion wouldn’t necessarily be universal since it was only open to men (as far as we know historically), though Mithra as a regular god (and I assume he had non-Mithraic cults/priesthoods for everyone) was openly worshipped by everyone. The Greeks and Romans believed most (not all but most) foreign gods were different aspects of their own.
