The meaning of the group as a whole can, however, be explained by the documents of the later Persian religion. The _Bundahish_ tells us that Ahura Mazda created before all things the Bull Goshurun, who was killed by Ahriman, the god of evil, and that from his side came forth Gayômort, first of men, while from his tail there issued useful seed-plants and trees, from his blood the vine, and from his seed the different kinds of beasts[869]. Save that the bull-slayer is here not the god of evil but the lord of light himself, the myth is evidently the same in the Mithraic bas-reliefs, for in some of the earliest monuments the Bull’s tail is actually shown sprouting into ears of wheat, while in others the production of animals as a consequence of the Bull’s death may be indicated, as well as the birth of the vine[870]. That the dog plays the part of the guardian of the Bull’s soul is probable from what we know of later Persian beliefs[871], while the scorpion as the creature of Ahriman may be here represented as poisoning the seed of future life at its source[872]. That Mithras is not supposed to kill the Bull from enmity or other personal reasons, but in obedience to orders from some higher power, is shown by the listening pose of his head during the sacrifice. This is M. Cumont’s opinion[873], as also that the serpent here takes no active part in the affair, but is merely a symbolic representation of the earth[874]. The whole drama is clearly shown as taking place in a cave or grotto, as appears from the arch of rocks which surmounts, and, as it were, acts as a frame to, the Tauroctony or bull-slaying scene in most Mithraic chapels. This cave, according to Porphyry, represents the universe.