The Mysteries of Eleusis were the most celebrated religious rites of ancient Greece. In the Eleusinian Mysteries, "τοὺς τελουμένους οὐ μαθεῖν τι δεῖν, ἀλλὰ παθεῖν καὶ διατεθῆναι": the initiated, said Aristotle, were not supposed to learn anything, but to be affected in a certain way and to be put into a certain frame of mind. No thought or idea was imposed on them. The hierophants showed them certain holy objects, which they could not see elsewhere, and were revealed to them in dramatic form.
The "ἐποπτεία" [epopteia] was the second degree of initiation into the mysteries, but the ritual of its practices was and remains occult. During the epopteia, the initiates were supposed to be witnessing a revelation, an epiphany. The candidates for initiation should therefore see the hidden things which cannot be described with words. Also, it was forbidden to initiates to reveal the mystery, as this was considered a crime against its highest law. Aeschylus was subjected to a trial because in one of his now lost tragedies he showed on stage certain symbolic objects of the Eleusinian Mysteries. He exposed, that is, the One Image.
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Working non-stop on Romeo Castellucci's Gilgamesh, a masterpiece based on the Mysteries of Eleusis.
Read also: Eleni Papalexiou, "Nyx Teleia. Nella notte profonda del mondo greco antico" [A Descent into the Dark Depths of the Ancient Greek World], in Toccare il reale. L’arte di Romeo Castellucci, Piersandra Di Matteo (ed.), Napoli: Cronopio, 2015: 21-34.