thumb|247x247px|General view of the site of the Telesterion in [[Eleusis]]
thumb|200x200px|Another View of Telesterion (Initiation Hall), Center for the [[Eleusinian Mysteries, Eleusis]]
The Telesterion ("Initiation Hall" from Gr. τελείω, "to complete, to fulfill, to consecrate, to initiate") was a great hall and sanctuary in Eleusis, one of the primary centers of the Eleusinian Mysteries. The hall had a fifty-five yard square roof that could cover three-thousand people, but no one revealed what happened during these events beyond there being "something done, something said, and something shown". This building was built in the 7th century BCE and was an important site until it was destroyed in the 4th century CE. Devoted to Demeter and Persephone, these initiation ceremonies were the most sacred and ancient of all the religious rites celebrated in Greece.
History
It is disputed when the site of the Telesterion is believed to have been originally built. There is evidence to suggest that the temple was created in the 7th century BCE, but historians know that it was created at least by the time of the Homeric Hymn to Demeter (650–550 BCE).
It was destroyed by the Persians after the Battle of Thermopylae, when the Athenians withdrew to Salamis in 480 BCE 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 intended to be reconstructed by Kimon, but it was instead rebuilt some time later due to Pericles' influence.
At some point in the 5th century BCE, Iktinos, the great architect of the Parthenon, built the Telesterion big enough to hold thousands of people. Other architects who worked on the Telesterion were Coroebus and Metagenes of Athens. In about 318 BCE, Philon added a portico with twelve Doric columns.
The Telesterion continued to see use throughout the Roman period. In 170 CE, 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 dispatching general Vehilius Gratus Iulianus to Greece with emergency reinforcements, who eventually defeated the Costoboci. Marcus Aurelius then had the Telesterion rebuilt bigger than it had been before. Then only a few hundred years later in 396 CE, the forces of Alaric the Visigoth invaded the Eastern Roman Empire and ravaged Attica, destroying the Telesterion, which was never to be rebuilt.
It was said in myth that Herakles partook in the Eleusian Mysteries as part of the Labours of Hercules' twelfth labor in which he captured Cerberus, and during which he saw visions of both Persephone and Demeter. Visitors at the time would have observed both residual damage and partial repairs. Although the mud-brick wall had been breached by Persian battering rams, it had since been patched. A new section was also added to the northeast, designated for sanctuary-related functions.
Sound propagation within large architectural spaces faces several challenges. First, sound weakens as it travels over distance. Second, sound energy diffuses in multiple directions, causing reverberation. Third, tall spaces can produce echoes. Fourth, spacious and empty interiors lack sound-absorbing surfaces, which can diminish clarity. The Telesterion overcame these obstacles through thoughtful architectural choices and materials. Its walls were constructed with resonant stone, allowing for a bold, amplified sound. The walls of the Anaktoron also reflected and reinforced sound between speakers and their audience. The interior columns enhanced echo effects, while the stepped seating contributed to sound reflection back into the space. The roof, made of wood, a naturally sound-absorbing material, reflected only part of the sound energy, helping modulate the acoustics further. During this ritual, sacred objects were presented to them. These conditions are believed to have amplified a sense of group cohesion, as participants were physically gathered in close proximity with limited individual visibility. The darkness likely obscured the view of the rituals about to take place, while the seating arrangement, facing inward toward the center of the hall, reinforced the feeling of collective participation in a shared experience.