Eleusinian mysteries

The Eleusinian Mysteries (Greek: Ἐλευσίνια Μυστήρια) were initiations held every year for the cult of Demeter and Persephone based at Eleusis in ancient Greece. They are the "most famous of the secret religious rites of ancient Greece". It is thought that their basis was an old agrarian cult which probably goes back to the Mycenean period (c. 1600 – 1100 BC) and it is believed that the cult of Demeter was established in 1500 BC. The mysteries represented the myth of the abduction of Persephone from her mother Demeter by the king of the underworld Hades, in a cycle with three phases, the "descent" (loss), the "search" and the "ascent", with the main theme the "ascent" of Persephone and the reunion with her mother. It was a major festival during the Hellenic era, and later spread to Rome. The name of the town, Eleusís, seems to be Pre-Greek and it is probably a counterpart with Elysium and the goddess Eileithyia.

The rites, ceremonies, and beliefs were kept secret and consistently preserved from antiquity. The initiated believed that they would have a reward in the afterlife. There are many paintings and pieces of pottery that depict various aspects of the Mysteries. Since the Mysteries involved visions and conjuring of an afterlife, some scholars believe that the power and longevity of the Eleusinian Mysteries came from psychedelic drugs.

Eleusinian Mysteries (Greek: Ἐλευσίνια Μυστήρια) was the name of the mysteries of the city Eleusis. The name of the city Eleusis is Pre-Greek, and may be related with the name of the goddess Eileithyia, but this is debated. The ancient Greek word "mystery" (μυστήριον) means "mystery or secret rite" and is related with the verb mueō (μυέω), which means initiation into the mysteries, and the noun mustēs (μύστης), which means one initiated. The word mustikós (μυστικός) means "connected with the mysteries", or "private, secret" (as in Modern Greek).

...
Wikipedia