The Function of the Tragic Greek Chorus

What do we know for a certainty about the tragic Greek chorus? We know that it numbered fifty at the beginning of the 5th century B.C.; we know that it was probably Aeschylus who lowered that number to twelve, and it was probably Sophocles who raised that number to fifteen, where it stayed for the remainder of the century. We know that the chorus was confined, either completely or mainly, to that part of the theatre known as the orchestra, and since the meaning of that word is dancing place, we can only conclude that dancing was a major part of what the chorus did. But of greater significance, we know that the poets considered the chorus extremely important; we know that, if for no other reason, because all of the extant tragedies contain choruses, and because of the large number of lines given to the choruses. If there is a direct correlation between the number of lines and the importance attached to the chorus by authors, then Aeschylus considered the chorus more important than either Sophocles or Euripides, but clearly they all considered the chorus important.