The Eleusinian Mysteries were initiation ceremonies held every year for the cult of Demeter and Persephone based at Eleusis in ancient Greece. Of all the mysteries celebrated in ancient times, these were held to be the ones of greatest importance. It is acknowledged 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 idea of immortality which appears in syncretistic religions of antiquity was introduced in late antiquity. 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 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 Elysion and the goddess Eileithyia.
The rites, ceremonies, and beliefs were kept secret and consistently preserved from a hoary 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 agents.

The Eleusinian Mysteries are believed to be of considerable antiquity, deriving from religious practice of the Mycenaean period and thus predating the Greek Dark Ages. One line of thought by modern scholars has been that these Mysteries were intended "to elevate man above the human sphere into the divine and to assure his redemption by making him a god and so conferring immortality upon him." Comparative study shows significant parallels between these Greek rituals and similar system—some of them older—in Near East (see Religions of the Ancient Near East).
These cults are the mysteries of Isis and Osiris in Egypt, the Adoniac of Syrian cults, the Persian mysteries and the Phrygian Cabirian mysteries. Some scholars argued that the Eleusinian cult was a continuation of a Minoan cult, probably affected by Near East.
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The idea of immortality which appears in syncretistic religions of antiquity was introduced in late antiquity. 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 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 Elysion and the goddess Eileithyia.
The rites, ceremonies, and beliefs were kept secret and consistently preserved from a hoary 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 agents.

The Eleusinian Mysteries are believed to be of considerable antiquity, deriving from religious practice of the Mycenaean period and thus predating the Greek Dark Ages. One line of thought by modern scholars has been that these Mysteries were intended "to elevate man above the human sphere into the divine and to assure his redemption by making him a god and so conferring immortality upon him." Comparative study shows significant parallels between these Greek rituals and similar system—some of them older—in Near East (see Religions of the Ancient Near East).
These cults are the mysteries of Isis and Osiris in Egypt, the Adoniac of Syrian cults, the Persian mysteries and the Phrygian Cabirian mysteries. Some scholars argued that the Eleusinian cult was a continuation of a Minoan cult, probably affected by Near East.
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