The construction of the cavea is dated between 367 and 330 BC. This period coincides with the activity of the Olympic champion, Antiochus of Lepreum, who dedicated the proedries (seats of honor) of the cavea, as recorded in the inscriptions preserved on their backrests.
The theatre was originally built without a permanent stage building (skene). This ensured that the propylon of the Thersilion remained visible from the cavea of the theatre. The Thersilion was the assembly hall of the Arcadian ...

The Thersilion was the assembly hall (bouleuterion) of the Arcadian League, where the Myrioi—the 10,000 delegates of the Arcadian Federation—convened. It was named after its donor and dedicator, Thersilos of Orchomenos. It was among the first buildings constructed in the city, consisting of a rectangular hypostyle hall with a roof, measuring 66.65 x 52.43 meters. The interior columns were arranged radially, and the floor sloped gently toward the center to ensure clear sightlines to the speaker's ...