The cult of Demeter in Eleusis began as a local religious festival under the control of the city's aristocratic families. When, however, Eleusis came under the power of the Athenians, the cult of Demeter was integrated into the official religious and ritual program of Athens. The general management of the Mysteries passed to Archon Basileus, who was responsible for the observance of traditional customs and ceremonies. On the first day of the celebration (15th of Boedromion / Agyrmos), the Archon Basileus invited the people of Athens to a festive assembly at the Poikile Stoa in the Agora to hear the prorrhesis, the official invitation to the faithful to participate in the Mysteries. On the 17th of Boedromion (Heireia Deuro), the Archon Basileus went to the City Eleusinion and offered the official sacrifice to the goddesses on behalf of the Boule and the Athenian demos.

Seats in hall of mysteries, once occupied by the wise and great (S.S.W.). Eleusis, 1907, photograph, Boston Public Library © Boston Public Library

The Archon Basileus also had the financial responsibility of the celebration and ensured that there would be enough animals for the sacrifices. His authority extended to the financial management of the sanctuary and its wealth. The Archon Basileus enjoyed the help and assistance of four “epimeletes of the Mysteries” in these areas. His role in maintaining order and protecting the sacred character of the Mysteries was vital. Two paredroi and heralds in the part of police officers kept the order during the celebration. The paredroi belonged to the entourage of the Archon Basileus, who reserved the right to remove them from office. They had to publicly account for their actions at the end of their term.

After the celebration and the return of the faithful to Athens (24th of Boedromion), the Archon Basileus appeared before the Boule of the Five Hundred, which met in the City Eleusinion and reported any serious offences committed in the previous days to impose the corresponding punishment. The punishment was severe, without excluding the death penalty or confiscating the accused’s property. The most famous cases concern the convictions of Alcibiades and Andocides for mocking the Mysteries. Even the unintentional violation of a rule could result in capital punishment.