This building has the shape of a small theatre with the stage building, seating places, and the orchestra. It had a double function in use. First, it was used as a Bouleuterion for the meetings of the Boules or the Senate. The second function was the Odeum as a concert hall for the performances. It was constructed in the 2nd century A.D by the order of Publius Vedius Antonius and his wife Flavia paiana, two wealthy citizens in Ephesus.
It had a capacity of 1500 spectators. It had 3 doors opening from the stage to the podium. The podium was narrow and one meter higher than the orchestra section. The stage building was two-storeyed and embellished with columns. The podium in front of the stage building and some parts of the seating were restored. The Odeon used to be enclosed with a wooden roof.
Two councils administrated Ephesus. These were Demos or the parliament which was open to the public was taken place in the great theatre and the Bouleia which gathered in this small theatre. The members of the boules were chosen from the aristocratic class of Ephesians. The most important decisions and city matters were discussed here.