The whole structure of the theatre, as well as the drama itself, may be traced to the chorus, whose station was the original centre of the whole performance. The orchestra, which occupied a circular level space in the centre of the building, grew out of the chorus or dancing-place of the Homeric times. The altar of Bacchus, around which the dithyrambic chorus danced in a circle, had given rise to a sort of raised platform in the centre of the orchestra, which served as a resting-place for the chorus. The chorus sang alone when the actors had quitted the stage, or alternately with the persons of the drama, and sometimes entered into dialogues with them. These persons represented heroes of the mythical world, whose whole aspect bespoke something mightier and more sublime than ordinary humanity, and it was the part of the chorus to show the impression made by the incidents of the drama on lower and feebler minds, and thus, as it were, to interpret them to the audience, with whom they owned a more kindred nature. The ancient stage was remarkably long, and of little depth; it was called the _proscenium_, because it was in front of the _scene_. _Scene_ properly means _tent_ or _hut_, such as originally marked the dwelling of the principal person. This hut at length gave place to a stately scene, enriched with architectural decorations, yet its purpose remained the same. We have seen how a single actor was added to the chorus by Thespis, who caused him to represent in succession all the persons of the drama. Aeschylus added a second actor in order to obtain the contrast of two acting persons on the stage; even Sophocles did not venture beyond the introduction of a third. But the ancients laid more stress upon the precise number and mutual relations of these actors than can here be explained. 4. THE TRAGIC POETS.--Aeschylus (525-477 B.C.), like almost all the great masters of poetry in ancient Greece, was a poet by profession, and from the great improvements which he introduced into tragedy he was regarded by the Athenians as its founder. Of the seventy tragedies which he is said to have written, only seven are extant. Of these, the "Prometheus" is beyond all question his greatest work. The genius of Aeschylus inclined rather to the awful and sublime, than to the tender and pathetic. He excels in representing the superhuman, in depicting demigods and heroes, and in tracing the irresistible march of fate. The depth of poetical feeling in him is accompanied with intense and philosophical thought; he does not merely represent individual tragical events, but he recurs to the greater elements of tragedy--the subjection of the gods and Titans, and the original dignity and greatness of nature and of man. He delights to portray this gigantic strength, as in his Prometheus chained and tortured, but invincible; and these representations have a moral sublimity far above mere poetic beauty. His tragedies were at once political, patriotic, and religious.