“An ancient oracle at Delphi, on the southern slope of Mount Parnassus. It was of extremely ancient origin, having originally belonged to a chthonic deity. Aeschylus’ claim in the Eumenides that it belonged successively to Ge, Themis and Phoebe—two of whom, at least, were earth goddesses—may not be far from wrong. In later times, the oracle was taken over by Apollo, who, according to the Homeric Hymn to Pythian Apollo, killed a python, a sacred snake associated with the oracle. The oracular utterances were made by the Pythia, a priestess who sat on a tripod over a cleft in the rock. Her incomprehensible mouthings were interpreted by a priest.
Although there were many oracles in the Greek world, the Delphic oracle was regarded as the final authority in religious matters. A great many of the most famous Greek myths involve the working out of the oracles that issued from Delphi. Associated with the shrine was the omphalos, a sacred stone that was regarded as the navel of the world, though various other centers made the same claim. Some authorities believe that the omphalos was the phallic cap of a tomb, possibly that of the python, since many oracles were associated with the tombs of heroes. In the first part of the Eumenides Orestes clings to the omphalos in seeking sanctuary from the Erinyes, or furies.”
Excerpted from: Murphy, Bruce, ed. Benet’s Reader’s Encyclopedia, Fourth Edition. New York: Harper Collins, 1996.