Up to the point when Sophocles imported his innovations in drama, the chorus had 12 members. Sophocles added three more. The 15 members of the chorus were entering the orchestra in rows ( usually face=3, depth=5 ), which means that although in old dithyramb the chorus was making a circle, in ancient theater the chorus was making squares. The leader of the chorus ("Coryphaios") was in the middle of the first row. Coryphaios was a professional dancer and singer. The rest of the chorus consisted of amatures chosen by the poet and payed by the sponsor (choregos)
The chorus was entering from the two "parodoi". His appearance was depending on the play. For the tragedy the chorus was very solemn and it was called "emmelia". In comedies it was funny and it was called "codrax", when in satiric drama it was scoptic and it was called "sicinnis".
The chorus, was considered to be the mouthpiece of society (in its humble form) and morality, and they were suffering along with the heroes. Its role (very important at first) was fading during the time."