http://agathe.gr/democracy/the_ekklesia.html
The Ekklesia (Citizens' Assembly) All Athenian citizens had the right to attend and vote in the Ekklesia, a full popular assembly which met about every 10 days. All decrees (psephismata) were ratified ... In this early form the seating capacity was about 5,000. ... In phase II (about 404/3 B.C.) an embankment with a retaining wall at the bottom created an auditorium with a slope contrary to that of the natural hillside, so that the audience now faced southwest and was sheltered from the winds. ... Two large stoas were begun but never finished on the south side of the Pnyx adjacent to the city wall. Visible today are the foundation of the curved retaining wall of the auditorium of phase III and the rock-cut bema (stand for speakers), which projects from the scarp.