The play now moves to its awful climax. The sight of Io stirs Prometheus to prophesy more clearly the end in store for Zeus. There would be born one to discover a terror far greater than the thunderbolt, and smite Zeus and his brother Poseidon into utter slavery. On hearing this Zeus sends from heaven his messenger Hermes to demand fuller knowledge of this new monarch. Disdaining his threats, Prometheus mocks the new gods and defies their ruler to do his worst. Hermes then delivers his warning. Prometheus would be overwhelmed with the terrors of thunder and lightning, while the red eagle would tear out his heart unceasingly till one should arise to inherit his agonies, descending to the depths of Tartarus. He advises the Chorus to depart from the rebel, lest they too should share in the vengeance. They remain faithful to Prometheus, ready to suffer with him; then descend the thunderings and lightnings, the mountains rock, the winds roar, and the sky is confounded with sea; the dread agony has begun. Once more the bold originality of Aeschylus displays itself. Here is a theme unique in Greek literature. The strife between the two races of gods opens out a vista of the world ages before man was created. It will provide a solution to a very difficult problem which will confront us in a later play. The conflict between two stubborn wills is the source of a sublime tragedy in which our sympathies are with the sufferer; Zeus, who punishes Prometheus for "unjustly" helping mortals, himself falls below the level of human morality; he is tyrannous, ungrateful and revengeful--in short, he displays all the wrong-headedness of a new ruler. No doubt in the sequel these defects would have disappeared; experience would have induced a kindlier temper and the sense of an impending doom would have made it essential for him to relent in order to learn the great secret about his successor. Pathos is repeatedly appealed to in the play. Hephaestus is one of the kindliest figures in Greek tragedy; the noble-hearted young goddesses cannot fail to hold our affection. They are the most human Chorus in all drama; their entry is admirable; in the sequel we should have found them still near Prometheus after his cycle of tortures. But the subject-matter is calculated to win the admiration of all humanity; it is the persecution of him to whom on Greek principles mankind owes all that it is of value in its civilisation. We cannot help thinking of another God, racked and tormented and nailed to a cross of shame to save the race He loved. The very power and majesty of Aeschylus' work has made it difficult for successors to imitate him; few can hope to equal his sublime grandeur; Shelley attempted it in his _Prometheus Unbound_, but his Prometheus becomes abstract Humanity, ceasing to be a character, while his play is really a mere poem celebrating the inevitable victory of man over the evils of his environment and picturing the return of an age of happiness.