As a prelude to our story we must glance at the mythical history of OEdipus, which, like that of his noble daughter, has been celebrated in ancient drama. An oracle had declared that he should kill his father, the king of Thebes. He was, in consequence, brought up in ignorance of his parentage, yet this led to the accomplishment of the oracle, for as a youth he, during a roadside squabble, killed his father not knowing him. For this crime, which had been one of their own devising, the gods, with their usual inconsistency, punished the land of Thebes; afflicting that hapless country with a terrible monster called the Sphinx, which had the face of a woman, the wings of a bird, and the body of a lion. This strangely made-up creature proposed a riddle to the Thebans, whose solution they were forced to try and give; and on every failure to give the correct answer she seized and devoured the unhappy aspirant. OEdipus arrived, in ignorance of the fact that he was the son of the late king. He quickly solved the riddle of the Sphinx, whereupon that monster committed suicide, and he was made king. He then married the queen,--not knowing that she was his own mother. [Illustration: OEDIPUS AND ANTIGONE.] This celebrated riddle of the Sphinx was not a very difficult one. It was as follows: "A being with four feet has two feet and three feet; but its feet vary, and when it has most it is weakest." The answer, as given by OEdipus, was "Man," who "First as a babe four-footed creeps on his way, Then, when full age cometh on, and the burden of years weighs full heavy, Bending his shoulders and neck, as a third foot useth his staff." When the truth became known--as truth was apt to become known when too late in old stories--the queen, Jocasta, mad with anguish, hanged herself, and OEdipus, in wild despair, put out his eyes. The gods who had led him blindly into crime, now handed him over to punishment by the Furies,--the ancient goddesses of vengeance, whose mission it was to pursue the criminal with stinging whips. The tragic events which followed arose from the curse of the afflicted OEdipus. He had two sons, Polynikes and Eteocles, who twice offended him without intention, and whom he, frenzied by his troubles, twice bitterly cursed, praying to the gods that they might perish by each other's hands. OEdipus afterwards obtained the pardon of the gods for his involuntary crime, and died in exile, leaving Creon, the brother of Jocasta, on the throne. But though he was dead, his curse kept alive, and brought on new matter of dire moment. It began its work in a quarrel between the two sons as to who should succeed their uncle as king of Thebes. Polynikes was in the wrong, and was forced to leave Thebes, while Eteocles remained. The exiled prince sought the court of Adrastus, king of Argos, who gave him his daughter in marriage, and agreed to assist in restoring him to his native country.