At Delphi, Greece, there is a white marble egg-shaped stone encircled by a python, or serpent, called 'Omphalos' which means navel in Greek. Omphalos was considered to be the center of the then known world. A myth reveals that Zeus released two eagles to fly around the world; one flew east, the other west, and they met at Delphi, thus marking the center of the world. The python is associated with the worship of the earth mother, Gaia, who was the mother of Python. The oracle at Delphi was originally dedicated to gaia and the women who were prophetesses were called Pythia. The Pythia sat on a tripod situated over a fissure in the rocks that emitted volcanic gasses. The gasses caused the Pythia to enter into an hysterical trance. While entranced they pronounced incoherent words which were translated by priests for those who came to consult the oracle. Hera, wife of Zeus, became enraged when she found that Leto, another goddess, had become pregnant by Zeus and ordered Gaia to produce Python to pursue Leto to prevent her from bearing children. Poseidon intervened and allowed Leto to stop long enough on the island of Delos for her to give birth to Apollo and Artemis. Four days later. Apollo, not a full-grown adult, went to Delphi to find Python and slay him for plaguing his mother. Apollo killed Python with his arrows in the temple at Delphi. Pythian games were established to commemorate Apollo's victory over Python and to celebrate the arrival of pilgrims from all over the world to seek the advice of the oracle at Delphi. Followers of Apollo practice tolerance, and balance. They even permitted the Cult of Dionysus, a god of hedonistic nature that practices orgiastic rites, to share the sanctuary site. Between December and February Apollo left Delphi for the land of the Hyperboreans, a place of never-ending day and eternal spring. During this time the oracle was silent, but festivals to Dionysus flourished. The shedding of the serpent's skin symbolizes re-birth and healing and was considered good luck. The symbol of the medical profession, the Caduceus, is a winged-staff with two snakes entwined around it.