But in the ancient theatre the impression produced must have been far more vivid, as one play followed another upon the stage, and the dark scenes of guilt were unfolded in due sequence before the very eyes of the audience. Apart from the Oresteia, very little is recorded about the tetralogies written by Aeschylus. He is known to have composed a Lycurgeia, on the fate of Lycurgus, the Thracian king and opponent of Bacchus; and an Oedipodeia, on the fortunes of the house of Oedipus. It is also fairly certain that he treated the legends about Hector, Ajax, Prometheus, and the daughters of Danaus in trilogic form. But these are the only instances for which there is clear evidence. No doubt most of his plays were written as tetralogies. Still, he does not seem to have adhered to the system on every occasion. The plays which he exhibited in 472—the Phineus, Persae, Glaucus, and satyric drama Prometheus—had apparently no connexion with one another.[58] There are also, among the titles of his lost dramas, several, such as the Sisyphus and the Atalanta, which seem to stand in an isolated position, and to be hardly capable of combination. In some cases, again, he may have adopted the tetralogic form only in part. The three tragedies may have formed a trilogy, while the concluding satyric drama was on a different subject. Thus the satyric Prometheus was produced, not with the Promethean trilogy, as we should have expected, but in a different combination altogether. There is no less uncertainty as to the structure of the lost tetralogies. It would be a mistake to assume that they were all as perfect in arrangement as the Oresteia. Even from the few remains and notices preserved we can see that the tetralogy was a flexible form of art, and could be treated in various ways. The connexion between the parts might be tightened or relaxed at will. In the Theban trilogy—the Laius, Oedipus, and Septem contra Thebas—there was a long lapse of years between the separate plays. In the Oresteia the intervals of time are much shorter. In the Lycurgeia, which described the invasion of Thrace by Dionysus, his defeat, capture, and final victory, the three plays followed so closely in point of time, that they must have been like successive acts in a single drama. Again, the trilogies might differ in respect of artistic completeness. The Oresteia forms a perfect whole. The legend is traced to its conclusion, and ends satisfactorily with the purification of Orestes. But the Theban trilogy was treated more in the chronicle fashion. It closed abruptly at a point where the course of events was still unfinished. The final scene of the Septem is full of forebodings of impending calamity. So marked is this feature, that before the discovery in recent years of the record which proves that the Septem was the last play of the three, all critics were agreed that it must have been followed by another tragedy.[59] This example shows us the necessity of caution in dealing with the whole