(en) The great hall in Eleusis, Telesterion ("Initiation Hall" from Gr. τελείω, to complete, to fulfill, to consecrate, to initiate) was one of the primary centers of the Eleusinian Mysteries. Devoted to Demeter and Persephone, these initiation ceremonies were the most sacred and ancient of all the religious rites celebrated in Greece. At some point in the 5th century BC, Iktinos, the great architect of the Parthenon, built the Telesterion big enough to hold thousands of people. In about 318 BC, Philon added a portico with twelve Doric columns. The site of the Telesterion is believed to have had some temple since the 7th century BC, or the time of the Homeric Hymns to Demeter (650-550 BC); the Telesterion had ten different building phases. The Athenians used several calendars, each for different purposes. The festival of Eleusinia was celebrated each year in Eleusis and Athens for nine days from the 15th to the 23rd of the month of Boedromion (in September or October of the Gregorian calendar); because the festival calendar had 12 lunar months, the celebrations were not strictly calibrated to a year of 365 days.

During the festival, Athens was crowded with visitors. As the climax of the ceremonies at Eleusis, the initiates entered the Telesterion where they were shown the sacred relics of Demeter and the priestesses revealed their visions of the holy night (probably a fire that represented the possibility of life after death). This was the most secretive part of the Mysteries and those who had been initiated were forbidden to ever speak of the events that took place in the Telesterion. It was destroyed by the Persians after the Battle of Thermopylae, when the Athenians withdrew to Salamis in 480 BC and all of Boeotia and Attica fell to the Persian army, who captured and burnt Athens. After the defeat of the Persians, the Telesterion was rebuilt some time later by Pericles. In AD 170, during the rule of Roman emperor Marcus Aurelius, an ancient tribe called the Costoboci launched an invasion of Roman territory south of the Danube, entering Thracia and ravaging the provinces of Macedonia and Achaea (Greece). The Costoboci reached as far south as Eleusis, where they destroyed the Telesterion. The emperor responded by despatching general Vehilius Gratus Iulianus to Greece with emergency reinforcements, who eventually defeated the Costoboci. Marcus Aurelius then had the Telesterion rebuilt. In AD 396, the forces of Alaric the Visigoth invaded the Eastern Roman Empire and ravaged Attica, destroying the Telesterion, which was never to be rebuilt.

(fr) La grande salle d'Éleusis, le Télestérion ("salle d'initiation", du grec τελείω "accomplir, initier") était l'un des principaux centres des mystères d'Éleusis. Consacrées à Déméter et Perséphone, ces cérémonies d'initiation étaient le plus sacré et le plus ancien de tous les rites religieux célébrés en Grèce. Au Ve siècle avant J.-C., Ictinos, le grand architecte du Parthénon, construisit le Télestérion, grande salle capable d'accueillir des milliers de personnes. Vers -318, Philon ajouta un portique à douze colonnes doriques. Le site du Télestérion a probablement abrité un temple dès le VIIe siècle avant J.-C., à l'époque des Hymnes homériques à Déméter (vers -650 / -550). Le Télestérion a connu dix phases de construction différentes. Les Athéniens avaient plusieurs calendriers, chacun à des fins différentes. La fête des Éleusinies était célébrée chaque année à Éleusis et à Athènes pendant neuf jours, du 15 au 23 du mois de boedromion (en septembre ou octobre du calendrier grégorien) : le calendrier des fêtes ayant 12 mois lunaires, les célébrations ne correspondaient pas strictement à une année de 365 jours.