Many ancient Hellenic religious traditions--and especialy Mystery Traditions--have 'hiera' (ἱερὰ), sacred objects. These objects are usually tucked away in a basket or box and only taken out (if at all) at very specific, very special occasion. The Eleusinian Mysteries had their own hiera, and they were a large part of the rites.

On the first day of the Myteries, the 14th of Boedromion, the priestesses of Demeter and Persephone took the basket of the hiera of Demeter from Her temple in Eleusis to Athens, and carried it on their heads along the Sacred Way (Ἱερὰ Ὁδός, 'Hieros Hodos') that initiates themselves would walk in a few days. The procession along the twelve miles of the Sacred Way, accompanied by an honor guard from Athens and villagers, would have arrived at Athens at the end of the day, no doubt being welcomed by celebrants already in the city. A priest of Demeter climbed up to the Akropolis to announce the arrival of Demeter’s sacred objects and her entourage, to the priestess of Athena. In this way, the relationship of these two Goddesses and of their two, once independent regions, were accorded mutual respect. It's interesting to note that Athena had Her own hiera, which featured heavily in the Arrephoria festival. That night, the procession of priestesses, priests, initiates, and other celebrants would have paraded through the Agora up to the sacred precinct of Demeter in Athens, called the Eleusinion, between the Agora and the north slope of the Akropolis. There, the hiera would have been taken into her temple, with singing and dancing.

On day five, many thousands of celebrants joined the pompe--procession--from Athens to Eleusis, led by the priestesses of Demeter and Persephone carrying the basket of hiera. Celebrants left early in the morning from Athens’ sacred gate at the northeast corner of the Agora) and proceeded along the Hieros Hodos to Eleusis.

On 20th and 21st of Boedromion, the initiates entered a great hall called Telesterion; in the center stood the Anaktoron ('palace'), which only the hierophants could enter, where sacred objects were stored. Before mystai could enter the Telesterion, they would recite a line that shows the hiera have made another appearance before this time. From Clement of Alexandrias 'Exhortation to the Greeks':

"And the formula of the Eleusinian mysteries is as follows: 'I fasted; I drank the draught; I took from the chest; having done my task, I placed in the basket, and from the basket into the chest.'"

We do not know what the hiera were. The content of the kiste, a sacred chest, and the kalathos, a lidded basket was a well-guarded secret. It would have been shown to initiates during the initiation, but they were sworn to secrecy. Thomas Taylor, in his 'Eleusinian and Bacchic Mysteries' says the hiera were 'a golden mystical serpent, an egg, a phallus, and possibly also seeds sacred to Demeter'. There is no further source listed.

For our rites for the Mysteries, the hiera do not make an appearacne. We do not know what they are, and so we cannot recreate even the idea of them. The hiera will most likely always remain an intriguing mystery about the Mysteries, one I would love to find out more about.