The Gases Under Delphi

In 1904 a scholar named A. P. Oppé published an article that killed a story for ninety years.

The French had been digging at Delphi since the 1890s. They had moved an entire village to do it. And under the temple of Apollo, where the ancient sources said there was a chasm breathing out vapour, they found no chasm. Oppé drew the obvious conclusion: the vapour was a literary invention, repeated by writers who had never checked, and the modern habit of taking it seriously should stop.

That was the consensus for most of the twentieth century. The ancient accounts were wrong, and anyone still talking about fumes at Delphi was being credulous.

What the ancient sources actually claim

It's worth being precise about what was being dismissed, because it is less lurid than the version that circulates.

Plutarch is the key witness, and an unusually good one: he served as a priest at Delphi. He describes a pneuma in the temple, a breath or exhalation, and says it sometimes carried a sweet smell, like expensive perfume. He says it was intermittent, that it varied in strength, and that in his own time it was fading.

He does not say it made the Pythia rave. He is, in fact, doing something rather sophisticated: offering a physical mechanism by which the god's influence reached her, in an essay whose subject is why the oracles were dying out.

Strabo, earlier, mentions a chasm and a vapour more briefly, and he had not been there.

So the textual foundation is real but narrow. One priest describing his own sanctuary in its decline, and one geographer summarising.

Two faults, crossing

In the 1990s a team went back to the question with different equipment.

Jelle de Boer, a geologist, had noticed years earlier that the Delphi region is cut by an active fault. Working with the archaeologist John Hale, he mapped a second fault running roughly perpendicular to it, and the two intersect beneath the temple.

That is a genuinely striking result, because intersecting faults are exactly where gases find a path upward. The local bedrock is bituminous limestone: rock with hydrocarbons in it, which release gas when heated and fractured.

The team sampled the spring water and the travertine deposits around the sanctuary and found light hydrocarbon gases: methane, ethane, and, in the water, ethylene.

Ethylene is the interesting one. It's sweet-smelling. It was used as a surgical anaesthetic in the 1920s and 1930s, and at doses below anaesthesia it produces euphoria, disinhibition and a floating detachment while leaving the patient able to talk.

A gas that smells sweet, comes out of the ground in fits and starts, and makes people euphoric but conversational. Against Plutarch's description, that's a remarkable fit. The findings were published in Geology in 2001 and defended at length the following year, and they went round the world.

Where it stops working

In 2007 the classicist Daryn Lehoux and the toxicologist Jonathan Foster went through the case properly, and the objections are not easy to wave away.

The first is dose. Ethylene's euphoric effects need it to make up a serious fraction of the air being breathed: percentage points, not traces. That is an enormous amount of gas to accumulate in a stone room that was not sealed, that people walked in and out of, and that had to stay at that concentration for the length of a consultation.

And it is not a private effect. Attendants stood in that room. Consultants entered it. If the chamber held enough ethylene to alter the Pythia's state, it would have altered everyone else's too, and nobody mentions that.

The second objection is about the samples. Ethylene was not detected in the travertine, the rock record of what the springs had been depositing over centuries. What turned up there was methane and ethane. The response from de Boer's team is that ethylene is chemically reactive and would have degraded into exactly those compounds. Which is true, and also unfalsifiable in this form: the absence of the key gas is accounted for by the properties of the key gas. Lehoux's verdict was that the reply was suggestive rather than substantive.

The third objection is the one with the longest reach. Foster and Lehoux argue that the case was persuasive mainly because of its shape: several independent-sounding disciplines converging on a conclusion, which reads like corroboration even when each strand is individually weak. Faults exist; hydrocarbons exist; ethylene does that to people; Plutarch mentions a sweet smell. Line those up and the conclusion feels irresistible. Examine them one at a time and none of them establishes that any gas reached the Pythia in a dose that mattered.

The honest position

Not debunked. Not demonstrated. Genuinely open, and probably not resolvable with what we can measure now.

The geology stands. Delphi does sit on intersecting active faults in gas-bearing rock, and Oppé's confident 1904 dismissal has not aged well. The ancient writers were describing something about that place that turned out to have a physical basis. That is a real gain, and it should make anyone slower to call an ancient source fictional just because a first excavation found nothing.

What hasn't been shown is the part that carries the whole story.

This is the same shape of argument as the ergot theory of the Eleusinian kykeon, and it ends in the same place, for the same reason. In both cases a plausible chemical exists, a plausible route exists, and the actual demonstration, this substance at this dose in these people, is missing.

There's also a question worth asking about the question. "Was she drugged?" assumes that finding a compound would explain the institution.

It wouldn't. The oracle operated nine days a year, on a published fee scale, with a formal priority list and a vetting ritual involving a goat. States came to it to authorise colonies and settle cult disputes. None of that is explained by a gas, and none of it would work differently if the gas were proven tomorrow.

The vapour, if it was there, was one component of an institution that ran on procedure, reputation and accumulated information, not the secret behind it. Two faults cross under a temple floor in Greece. That much we know.