From some source I quoted: The Bouleuterion doubled as an Odeion. It was built in the second century AD by Publius Vedius Antoninus and his wife. It was used both for meetings concerning city rule (as a bouleuterion or “city hall”) and for performances of music or oratory. It could hold 1400 spectators.

From the Wikipedia: The Odeon was a small roofed theater constructed by Vedius Antonius and his wife around 150 AD. It was a small salon for plays and concerts, seating about 1,500 people. There were 22 stairs in the theater. The upper part of the theater was decorated with red granite pillars in the Corinthian style. The entrances were at both sides of the stage and reached by a few steps.