The senate house was builtin the 2nd century B.C. by Timarchos and Heraklides of Miletus. The construction of the bouleterion was financed by the Syrian Emperor Antiochos IV.
It was built in the form of a round theatre facing a semi-circular meeting hall. The building was 56m long. There was a large courtyard accessed through a monumental gate. The courtyard was surrounded by 28 columns on both sides.
At the center of this courtyard there was an altar for Artemis.
The base of the meeting hall is still clearly visible. Only 19 of the steps exist today. The Bouleterion had seating for 1200 people. The whole structure was covered by a saddleback roof.