Page "Leto" Paragraph 14

Another ancient earth creature that had to be overcome was the dragon Pytho, or Python, which lived in a cleft of the mother-rock beneath Delphi and beside the Castalian Spring.

Apollo slew it but had to do penance and be cleansed afterwards, since though Python was a child of Gaia, it was necessary that the ancient Delphic Oracle passed to the protection of the new god.