Bk VII:404-424 Medea attempts Theseus's life, then vanishes.
Now Theseus came to Athens, Aegeus's son, but as yet unknown to him. He, by his courage, had brought peace to the Isthmus between the two gulfs. Medea, seeking his destruction, prepared a mixture of poisonous aconite, she had brought with her from the coast of Scythia. This poison is said to have dripped from the teeth of Cerberus, the Echidnean dog. There is a dark cavern with a gaping mouth, and a path into the depths, up which Hercules, hero of Tiryns, dragged the dog, tied with steel chains, resisting and twisting its eyes away from the daylight and the shining rays. Cerberus, provoked to a rabid frenzy, filled all the air with his simultaneous three-headed howling, and spattered the green fields with white flecks of foam. These are supposed to have congealed and found food to multiply, gaining harmful strength from the rich soil. Because they are long-lived, springing from the hard rock, the country people call these shoots, of wolf-bane, "soil-less" aconites. Through his wife's cunning Aegeus, the father, himself offered the poison to his son, as if he were a stranger. Theseus, unwittingly, had taken the cup he was given in his right hand, when his father recognised the emblems of his own house, on the ivory hilt of his son's sword, and knocked the evil drink away from his mouth. But she escaped death, in a dark mist, raised by her incantations.