Explaining the Oracle's Visions

When John Hale was an archaeology graduate student at Cambridge University in the 1970s, he was taught that the ancient Greek accounts of the events and rituals at the Oracle of Delphi were fundamentally flawed.

A fifth-century B.C. representation of Aegeus, king of Athens, consulting the Delphic Oracle.

(The Gallery Collection/Corbis)

The Greek historian Plutarch had spoken of a spring that emitted "fragrance and breeze" into the Oracle's temple, driving the priestesses there into a frenzied trance and prompting them to deliver prophetic visions. But 19th- and 20th-century researchers, after decades of searching, found no physical evidence supporting Plutarch. "The French dug at Delphi in the 1890s and didn't find any gases," says Hale, director of liberal studies at the University of Louisville. "Other archaeologists had dug there and found no faults or springs."

But that's not the end of it. In the past 11 years, a series of more rigorous scientific investigations has challenged—and, in effect, reversed—the accepted orthodoxy, showing in modern detail how hydrocarbon gases, still present at the site, might explain the ancient Greek stories.

Credit for that goes to Hale and colleague Jelle de Boer, a Wesleyan University geologist, whose chance meeting led to research validating Plutarch's accounts. The two met in 1996 at a research site in Portugal; there, over a glass of wine, de Boer claimed to have seen a fault line at Delphi following an earthquake more than a decade earlier. Hale was skeptical. "This," he recalls thinking, "would rewrite archaeology, and Greek history, and its religion."

A deal was struck: They would travel to Delphi, to the rugged slopes of Mount Parnassus, and map out the terrain. They did and, on two separate trips, they discovered not one but two intersecting fault lines—the first running east-west (as suggested by de Boer), the second northwest-southeast. The base of the ancient temple stood squarely at their intersection. Recent seismic activity, they surmised, had revealed the hidden secret.

Fumes. The discovery of crisscrossing fault lines beneath the Oracle's grounds answered one question outright. If the gases of which Plutarch spoke were real, where did they come from? And it hinted at yet another: the unknown nature of their composition. De Boer posited that limestone deposits buried deep beneath the ground might have released hydrocarbon gases—specifically, methane, ethane, and ethylene—into the air.

Ethylene, in particular, piqued the researchers' interest. "Ethylene is what gives fruits their sweet smell," says Hale, "which seems to match the note that Plutarch had made of the odor [of the Oracle gases]." Ethylene also has a history of mental confabulation. "In low doses, ethylene can induce a trance," Hale says. "Early-20th-century researchers found that ethylene could produce an anesthetic state twice as fast as nitrous oxide."

The researchers contacted chemist Jeffrey Chanton of Florida State University to analyze water samples from natural springs discovered in the faults. The analysis detected low levels of ethylene, among other gases. "For the descriptions in the literature of what caused the [priestess] to come forward with her predictions, ethyl ene is the perfect gas," de Boer says.

Though scholars continue to debate the precise nature of the gas—an Italian team published a paper last year arguing that methane-induced oxygen deprivation was the culprit—Hale says the bigger point is that this debate is happening at all. "People were responding to very specific phenomena in the Earth's surface," he says. "Modern science confirms the validity of those ancient observations, and this is a great way of looking at ancient religion."