The steep, rocky slopes of Mount Parnassus seem to scrape the sky above me. I’m standing among the ruins of one of the most famous places in the ancient world. There’s something solemn and weighty about this place, as if gravity has been cranked up a few Newtons. I can feel history pressing down.

This is where Delphi’s famed oracle — an office held by a long line of high priestesses believed to be the mouthpiece of the god Apollo — for centuries answered questions from visitors near and far. Greeks called the location the “navel” of the world, represented by the Omphalos of Delphi, an ancient stone monument.

For 1,500 years, up through the time when Christianity became dominant, Delphi was one of the power centers of the world. That’s a lot of years. Even if you figure in the idea that oracles, with the right luck (and publicity), can be surefire attention grabbers, Delphi wasn’t top dog just because it was home to a prognosticator. There were lots of oracles in Greece and the rest of the ancient world for competition.

No, there was — and is — something special about Delphi.

Among the qualities that make it unique: a 1,500-year-long line of women hopped up on ethylene gas.

When traveling, some people prefer the blank-slate approach, arriving with fresh eyes and no preconceived notions. Not me. I would rather read voraciously about the places I plan to visit. Not just travel guides, but books that burrow beneath the status quo. Better yet, I love to read about a place when I’m actually there. Thanks to my trusty Kindle, in recent years I’ve been able to cart books around with me that are relevant to my itinerary without exceeding my baggage allowance.

There’s nothing quite like reading a chapter in a book about Delphi when you’re sitting on a rock, looking at Delphi.

For a trip to Greece last year, that book was William J. Broad’s “The Oracle: Ancient Delphi and the Science Behind Its Lost Secrets.” The author details the quest to confirm that the oracles of Delphi really did inhale mysterious vapors to achieve the trances they fell into while delivering their pronouncements — a notion that was laughed at by scholars until recent archaeological and geological discoveries.

I traveled in January, one of my favorite times to explore the world. The hotels were cheap, the weather doable (I lucked out with no snow), the crowds practically nonexistent. The itinerary included all the big sites in Athens, the noble ruins of Olympia, the ancient city of Mycenae and the spectacular monasteries built into the rock formations of Meteora.

But on this day, all my thoughts are of Delphi.

Ancient play set here

Much of what happened in Delphi has been lost in the mists of history, but we do know quite a lot, Broad reminds us in his book.

Euripides casts all the action in his play “Ion” in and around the temple of Apollo, whose foundation you can still see today. Herodotus, the father of history, describes how the Oracle’s guidance helped lead the Greeks to victory in the Persian wars. Though Greece didn’t have a national identity in the way we think of it today, Delphi served as a sort of spiritual capital: a no man’s land that became a de facto diplomatic mission to the rest of the known world. Considering all the traffic that came to Delphi from other countries seeking oracular wisdom, it’s no wonder that its news and gossip was the freshest.

Ancient literature describes in detail the process of how the oracle — known as Pythia, a woman at least 50 years old who was selected as a young girl for the office by the priests — received her inspiration. With much ritual, she went into a special chamber and sat on a tripod that was set over an opening in the earth known as the chasm. There she inhaled the famed vapors that sent her into a trance, then issued her prognostications.

Ancient ruins still shine

At Delphi you can climb up Mount Parnassus to the sanctuary’s ancient stadium high on a plateau. I look down on the Temple of Apollo. In the distance, three remaining Doric columns of the Tholos of Delphi, a circular building dedicated to Athena that must have astonished ancient visitors with its beauty, catch a glint of sun.

It is an unsettled day, weather-wise, and the back-and-forth between dark clouds and periodic shafts of sunlight add to the solemn, spiritual feel.

I ponder the mystery of the place. I wish more were known about how the oracle did her thing. Was she privy to all the information floating around Delphi? Was she a shrewd diplomat? Did she figure out ways to make her predictions just vague enough to keep people guessing? Were secret traditions and knowledge passed down from one oracle to the next, helping each one to conform to a sort of oracular standard?

Or was it all gibberish? Was it the priests who held the power, doing all the interpreting, using the oracles as mere mouthpieces? We don’t really know. Records don’t exist.

What we do know is that for centuries, Delphi was awash in riches. People paid for the chance to ask the oracle a question. City-states sent delegations to build temples and offer gifts.

Early Christians didn’t believe that the oracle was fake, Broad writes. They thought she was all too real, a manifestation of Satan on Earth. Eventually the temple and all the glory of Delphi was destroyed, and for more than a thousand years, the area was forgotten.

For more than 1,000 years, the “reputation” of Delphi took one hit after another. Despite the documentation of the ancients, with a number of sources talking about the vapors inhaled by the oracles, those accounts were dismissed. It was all a sham, people thought.

This thinking was reinforced when French archaeologists began excavating the site in 1892. They found no evidence of a cleft that would have let any type of gases escape. And, besides, what kind of gas would have been able to intoxicate just the oracle — without killing her — and not affect people in the next room?

For more than 100 years, throughout the modern era, there seemed to be no doubt: There was no physical explanation for the oracle. And there was no earthquake fault at that location that could have caused any sort of gas to seep out.

Then a geologist, an archaeologist, a chemist and a toxicologist got into the act.

A geologist’s discovery

The late Jelle Zeilinga de Boer, a geologist at Wesleyan University in Connecticut, was the pioneer. In the 1980s he was roaming the area of Delphi when he stumbled across a new cut in a road for a bus turnaround and discovered an active earthquake fault. Could that fault have been responsible for covering up the cleft in the Earth about which ancients spoke?

In his book, Broad treats the subsequent investigation as a kind of laid-back treasure hunt, with De Boer joining forces with John R. Hale, an archaeologist from the University of Louisville. It took years, but they were able to confirm their hypothesis. Rock samples, which the Greek government allowed to be analyzed, found traces of methane and ethane.

But what could intoxicate the oracle? It turned out the likeliest candidate is ethylene, a gas that doctors once used as an anesthetic but was abandoned because of its flammability. What’s more, ethylene can produce a high that still allows an inhaler to articulate words and phrases (though not necessarily totally cogent ones).

Eventually, the scientific community, even the reluctant French, grew to accept the conclusion that the ancient sources were accurate in describing the “trance” into which the oracle fell. It’s still a theory, of course. But an intriguing one.

Walking down the hill, I pause once more to look above me, at all that sky and rock bearing down, and I imagine I’m a traveler in the seventh century B.C. at the end of a journey that took perhaps weeks or months. Would I be given the nod by the priests to ask a question of the oracle?

I’m glad I did my homework. Knowing the intricate back story, Delphi has become so much more than another set of interesting ruins. I somehow belong on this place’s long and fascinating timeline. At the moment, I’m at the end of that line, of course, but also, as befitting the navel of the world, it feels like the beginning.