At the western extremity of the Prytaneum and behind the Sacred Stoa, is a rectangular hall, built in 220 B.C., with marble staircases on 3 sides. This building shows to advantage the remarkable skill and taste of the Prienian architects. This is the Ecclesiasterium, the meeting-place of the elected popular assembly. At the far end, there were sixteen benches, and on two of the other sides ten each. The fourth wall contains 2 doors and a big window. There is a large marble bench against the wall. In the center of this hall is an altar adorned with bulls-heads and laurel leaves.
The walls rose up above the steps. The ceiling was supported by four-cornered columns ornamented in the Doric style like the walls. This hall was accessible by several doors opening onto steps. These steps provide further seating for some 640 persons: here sat the members of the Assembly, while the benches were kept for the magistrates and important foreign guests. The orators stood between the benches and the altar. At the begining of every period of sessions of the Assembly, sumptuous sacrifices were offered before the altar. At the opening of each session, normal sacrifices were offered.
In this building the government of the democracy of Priene settled all the affairs of the city.