Since we have no exact information as to when the City Dionysia began or ended, we are in doubt as to its duration.[294] But it is probable that it lasted for six days, certainly five. The first day was occupied with the procession, as already described (see pp. 121 f., above). The second day, and possibly the third, was devoted to dithyrambs, the literary type from which tragedy had sprung. There were five choruses of boys and five of men, each of the ten tribes annually standing sponsor for one chorus. We happen to know that the contest of men was added to this festival in 508 B.C. Inasmuch as each chorus consisted of fifty amateur performers, it will be seen that no inconsiderable portion of the free population received every year a musical training which could not but enhance their appreciation of the choral and lyrical parts of the dramas and likewise improve the quality of the material from which the dramatic choruses were chosen. The last three days of the festival seem to have been given over to the dramatic performances, but just what the arrangements were is not known. In Aristophanes’ _Birds_, vss. 786 ff., the chorus, praising the use of wings, remarks that “if one of you spectators were so provided and became wearied with the tragic choruses, he might fly away home and dine and then fly back again to us.” From this passage it has been plausibly concluded that the comedies came later in the day than the tragedies. It would seem as if the three tragic playwrights must have produced their plays on as many successive mornings, the comedies following later each day in similar rotation. It is well known that at the City Dionysia each of three tragic poets brought out four plays in a series, three tragedies and one satyric drama (see pp. 23 f., above). Such a group was termed a _didascalia_ (“teaching”). It was Aeschylus’ frequent practice to have all four plays treat different aspects of the same general theme, the levity of the concluding piece counterbalancing somewhat the seriousness of the three tragedies. In that case the set of four was called a tetralogy; but if the satyric drama dealt with a different topic than the tragedies, the latter were said to form a trilogy. No tetralogy or didascalia is extant and only one trilogy, the _Agamemnon_, _Libation-Bearers_, and _Eumenides_, which Aeschylus brought out in 458 B.C. The satyric drama in this series is not preserved but was entitled _Proteus_. It may have dealt with the shipwreck of Menelaus, Agamemnon’s brother, on his return from Troy. After Aeschylus the four pieces in a didascalia were usually unrelated in subject.