The building of Thersileon adjacent the theatre of Megalopolis was an assembly hall erected ca 370 BC for the Arcadian League. Thersilion was known as the 'Hall of the Ten Thousand'. This sugested the capacity of the structure.Thersileon stood directly to the north of the theatre.The general plan consits of rows of columns and floor slopes in towards a flat off-centre rostrum.
- E. F. Benson, “The Thersilion at Megalopolis.” The Journal of Hellenic Studies, vol. 13, 1892, pp. 319–327