The priestess who delivered the oracle was historically called the Pythia. She spoke in a specially secluded area of the temple called the adyton, literally “not to be entered.”

It was the temple’s innermost sanctuary. Only the priestess delivering the oracle and the male priests who interpreted her speech could enter this secluded, airtight chamber. Numerous historical accounts give us a general picture: a fissure in the ground released strongly scented vapors.

Legend says that in remote antiquity, before Mount Parnassus became an oracular center, a shepherd’s goats inhaled the vapor and went mad. People discovered that those who breathed fumes rising from the earth experienced visions and uttered strange speech. At the time this was explained by saying, “The person has communicated with the god, and these words are teachings the god wishes to give believers.” That is why a center for Apollo’s oracle was established here.

Homer’s epics and The Histories by Herodotus, the father of history, provide many details about prophecies at Delphi. Most valuable of all, the ancient scholar Plutarch described many details late in life, and he himself was a priest at Delphi.

More than twenty years ago, around the year 2000, geologists from the University of Kentucky analyzed and surveyed the site.

They first found that it lay in a region of extremely active continental-plate movement. The African and Anatolian plates collide with the Eurasian plate, producing intense geological activity and many faults around the Aegean, including Turkey to the east and Greece to the west. Two faults supposedly crossed directly beneath the Temple of Apollo on Mount Parnassus. Major fault activity could cause underground gases to surge upward.