As recounted by Apollodorus in his Bibliotheca, Cadmus, the founder of Thebes, once come across a holy spring, from which he wished to draw water, for it was known that one who drank from it would acquire great wisdom. The spring was guarded by a terrible dragon, who killed scores upon scores of brave men and women. Yet Cadmus managed to defeat the beast.
Thereupon the goddess Athena revealed herself to Cadmus and said unto him: collect the dragon’s teeth and sow them as you would grains of corn, and you shall be greatly rewarded. And Cadmus did as the goddess instructed, and lo and behold, terrible armed warriors sprang up from the dragon’s teeth. Apollodorus calls them The Sown ones, or Spartoi, but they were called by many other names, such as Vrachoi, or 'Rocks', for they had emerged from among the rocks.
At first, Cadmus was grateful to the wise goddess, for he thought he would have a great army at his command. In time, though, he grew frightened of the fearsome warriors he had brought into this world and swore to slay them…