The chorus in Greek tragic plays was made of 13 singing and dancing members originally. The leader of the chorus interacted with the characters in the play, and spoke for the general population (the play's public opinion). The whole chorus tried to stay in rhythm with each other so they could be viewed as one entity rather than separate entities. After a while, the members of the chorus increased to 15, and the number of actors increased to three. Everything the chorus did was in song form. It was the author's job to choreograph the chorus.
