to enable an actor to be substituted for the lay figure of Prometheus. So long as the hero was fixed in his place, an actor concealed behind him experienced little difficulty in speaking his lines for him; but as the time drew near for his release a living impersonator was required. How was this substitution managed? I conceive that a wooden frame-work, rudely suggesting a rock, was propped up at the outer extremity of the orchestra. At the moment of the catastrophe the supports were removed and the structure allowed to collapse into the declivity. After an interval sufficient for the exchange had elapsed, the rocky background was once more raised into its place and braced. [Illustration: FIG. 71 AUDITORIUM AND ORCHESTRA OF THE THEATER AT THORICUS See p. 227, n. 1] About 465 B.C. an advance step in theatrical conditions was taken when a scene-building was erected immediately behind the orchestra, where the declivity had previously been (see p. 66, above). This first scene-building must have been very simple, probably of only one story, without either parascenia or proscenium (Fig. 74), and capable of being readily rebuilt so as to be accommodated to the needs of different plays. The extant dramas show that from the first the new background was pierced by at least one door and that the number was soon raised to three, though they were not all used in every production. The different doorways were conventionally thought of as leading into as many separate houses or buildings. Thus, whereas the actors had hitherto been able to enter and depart only through the two parodi, from one to three additional means of entrance were now provided. Moreover, the mere fact of having a background was no small advantage. For example, it enabled Aeschylus to introduce a distinct improvement in dramatic technique. Heretofore scenes of violence must either have been boldly enacted before the spectators’ eyes or reported by a messenger. Since the sacrosanctity of the actor while engaged in a performance and the Greeks’ aesthetic sense interfered with the first alternative (see pp. 127-32, above), doubtless the second had usually been resorted to. Now Aeschylus is said to have invented the very effective device of having a character killed behind the scenes during the play. In view of the physical conditions it will be understood that the failure of Aeschylus’ predecessors to avail themselves of this expedient was due to no lack of inventive genius on their part but simply to the entire absence in their time of a back scene to use for the purpose. It is not known just how long it took Aeschylus to discover this possibility in the new arrangements; but it was certainly not later than the _Agamemnon_ (458 B.C.), in which the king’s agonized death cries from behind the scenes (vss. 1343 and 1345) still have power to affect even modern audiences. Further modifications of this artifice have already been mentioned on p. 128.