The Bouleuterion (council or assembly house) is built on the side of the hill. The central hall has an area of 1250-1300 m2; the walls had a stone foundation (which survives) and an upper section made with unbaked bricks (now lost). Eight Ionic columns and 14 buttresses supported the roof. The members of the council sat on rough stone benches (some survive higher on the slope). The great stone altar near the south wall is dedicated to Zeus Naios (of the Naiads) and Bouleus (the Counselor), as well as Dione. Next to it were the wooden chairs for the speakers and a stone ballot stand for voting. The Bouleuterion was also used during the Naia Games for the trial of athletes who violated the rules.