The mystery religions were not religions per se, but rather secret
cults of the
Greek and then
Roman world. Their number included that of
Dionysus,
Demeter and
Persephone, and
Orpheus. A
Greek citizen, and then essentially anybody once the
Romans conquered
Greece, could be initiated into the cult of their choice.
Many have gone as far as to suggest that
Christianity borrowed or inherited much from the mystery religions. Fasting and confession of sin was sometimes done, and, some claim, even
baptism. Furthermore, some have pointed out that the mystery cult of
Dionysus has a story of
Dionysus very similar to that of
Jesus. The reply is usually that the ideas developed in parallel, and the fact that many religions all over the world have similar kind of things going on.
Though they spread like wildfire all over the known world once the
Romans conquered the
Greeks and
Hellenism became all the rage, nobody today is really sure what was up with the mystery religions. The reason for that is this: the punishment for divulging the cult's secrets was
death. Despite the hundreds of thousands of people initiated into the various cults, we still know little about them.