Jupiter, in the form of a bull, carries away Europa, who is the daughter of Agenor, the king of Phenicia. When her handmaidens tell Agenor of the kidnapping, he commands his son Cadmus to look for Europa and not to return until he finds her. Cadmus searches for his sister for many years and in strange lands. Although he searches diligently, killing many monsters and endangering himself many times in his quest, he cannot find her. Afraid to return to his father, he consults the oracle of Apollo at Delphi and asks where he should settle. The oracle tells him that he will find a cow in a field, and that he should follow her, for she will lead him to a good land. Where the cow stops, Cadmus is to build a great city and call it Thebes.
When Cadmus soon thereafter sees a cow, he follows her. Finally, the cow stops on the plain of Panope. To give thanks to the gods, Cadmus sends his slaves to find pure water for the sacrifice. In a dense grove, they find a wonderful clear spring, which is, however, guarded by a terrible dragon sacred to Mars. His scales shine like gold, his body is filled with a poisonous venom, and he has a triple tongue and three rows of huge, ragged teeth. The servants, thinking only to please their master, dip their pitchers in the water, whereupon all are instantly destroyed by the monster.
After waiting many hours for the return of his servants, Cadmus goes to the grove and finds the mangled bodies of his faithful slaves and, close by, the terrible monster of the spring. Cadmus throws a huge stone at the dragon, but the stone does not dent his shining scales. Then, he draws back his javelin and heaves it at the serpent. It goes through the scales and into the entrails. The monster, trying to draw out the weapon with his mouth, breaks the blade and leaves the point burning his flesh. He swells with rage as he advances toward the hero, and Cadmus retreats before him. Cadmus then throws his spear at the monster, and the weapon pins him against a tree until he dies.
As Cadmus stands gazing at the terrible creature, he hears the voice of the goddess Minerva telling him to sow the dragon’s teeth in a field. Hardly has he done so when a warrior in armor springs up from each tooth. Cadmus starts toward the warriors, thinking he must slay them all or lose his own life, but again Minerva speaks to him and tells him not to strike. The warriors begin to do battle among themselves. All are slain but five, who then present themselves to Cadmus and say that they will serve him. Together with these five warriors, Cadmus builds the city of Thebes.
Jupiter gives Cadmus Harmonia, the daughter of Mars and Venus, to be his wife, and the gods come down from Olympus to honor the couple. Vulcan forges a brilliant necklace with his own hands and gives it to the bride. Four children are born, and for a time Cadmus and Harmonia live happily with their children. Yet doom hangs over Cadmus and his family for the killing of the serpent. Eventually, Mars avenges himself by causing all of Cadmus’s children to perish.
In despair, Cadmus and Harmonia leave Thebes and go to the country of the Enchelians, who make Cadmus their king. However, Cadmus can find no peace because of Mars’s curse on him. One day, he tells Harmonia that if a serpent were so dear to the gods he himself wishes to become a serpent. No sooner does he speak the words than he begins to grow scales and to change his form. When Harmonia beholds her husband turned into a serpent, she prays to the gods for a like fate. Both become serpents, but they continue to love human beings and never do injury to anyone.