The Thebans in ancient days used to sacrifice bulls to Apollo of the Ashes. Once when the festival was being held, the hour of the sacrifice was near but those sent to fetch the bull had not arrived. And so, as a wagon happened to be near by, they sacrificed to the god one of the oxen, and ever since it has been the custom to sacrifice working oxen. The following story also is current among the Thebans. As Cadmus was leaving Delphi
by the road to Phocis
, a cow, it is said, guided him on his way. This cow was one bought from the herdsmen of Pelagon, and on each of her sides was a white mark like the orb of a full moon.