A Trip to Hell: Mysterious tunnel system and underground river at Baiae, Italy

Many people are familiar with the Oracle of Delphi, where Pythia, the priestess of Apollo was said to relate messages from the god to the temple visitors. The specialness of this place was recognized prior to it being a sacred place of Apollo. The Delphic fault emits hydrocarbon gases that affect animals and humans. But, the spookiness of Delphi will be reserved for another time. In this piece, I discovered what sounds to be likely another location of an Oracle, this time, an Oracle of the dead, and geology has everything to do with its origin.

In the December 2016 issue of Fortean Times [1], the article entitled “A Visit to the Underworld” by Mike Dash describes the Oracle of the Dead proposed at Baiae (Baia), a village on the northwest shore of the Bay of Naples in Italy. Baiae flourished due to its geographical location near Naples, the coastal setting, and its connection as part of Campania, a volcanic complex that includes the Phlegraean Fields and Mount Vesuvius. The Greeks settled the area, naming it Campi Flegrei or “burning fields” (now referred to often as the Phlegraean Fields) [2] – more details about this after I tell you about why a discovery at Baiae warranted its own piece in FT and my interest in declaring it “spooky”.


The location of Baiae is pinned. Vesuvius is directly east.


Entrance to the Cave of the Sibyl (Sybil)

Entrance to the Cave of the Sibyl

Dash’s piece describes a tunnel system into the cliffs at Baiae that remains mysterious and generally unstudied by archaeologists. Doc Paget (Dr. Robert Ferrand Paget) explored the system in the 1960s and concluded it was part of a Necromanteion – a temple where citizens could go to consult the dead. Keepers of such temples would create an elaborate system where visitors brave enough to undertake the ritual in order to speak to the dead would be purified with food and narcotic substances. An animal would be sacrificed. The participant would move through corridors and gates simulating a descent to the underworld (Hades). The most famous Necromanteion is that of Ephyra, in Greece. In 700-600 BC, the Greeks held the idea that more than one “navels of the earth” existed where you could access the underworld. Another of these connections to Greek Hell is proposed at the Ploutonion at Hieropolis in Turkey, where noxious gas emissions occur due to the volcanic plumbing. In this location, death was immediate due to the toxic smoke. People could not descend into the vaporous space. Volcanic areas of Greece, Turkey, and Italy lent themselves easily to an interpretation of the gates of Hell with their steaming fissures, sulfur smell, and hallucination-inducing (often toxic) gasses. It’s likely the Hellish nature of the Necromanteions were exaggerated with theatrics as well.

Philosophers of the time said an Oracle of the Dead existed in the Phlegraean Fields, near Lake Avernus (around Naples, Italy). Greeks settled the area due to the climate and good soil [2]. As with the Greek locations, this was a very active volcanic area with sulfur vents and boiling springs. The sibyl, a prophetess, was said to be the bridge between the voices of the living and dead. Several spots for the oracle were proposed. In 1932, Amedeo Maiuri discovered the Antro della Sibilla in Cuma which he interpreted to be the Cave of the Sibyl described in Virgil’s Aeneid. The chamber had been excavated into the volcanic deposits, accessed by a trapezoidal passage. Paget and Keith Jones searched a wide range around Avernus for other tunnels and discovered those hidden at Baiae.

From http://www.italysvolcanoes.com/. Showing locations of Lake Avernus, the mythical location of the Oracle of the Dead, and Cuma (location of Cave of the Sibyl) and Baiae.

From http://www.italysvolcanoes.com/. Geologic map showing locations of Lake Avernus, the mythical location of the Oracle of the Dead, Cuma (location of Cave of the Sibyl) and Baiae. Black lines are faults.

Discovery at Baiae

Baiae was a happening place during Greek and Roman times: Atlas Obscura refers to it as the “Las Vegas” of its day, particularly towards the end of the Roman Republic. The saunas and hot baths complimented the hedonistic reputation of the resort town. It later became part of Port Julius of the Roman Navy and finally was deserted. Parts of the city sunk several meters as a result of its location within an active volcanic caldera. Remains of the city can be seen via underwater excursions into the bay, a spooky side note unto itself.

Remains of the sunken great city of Baia.

Remains of the sunken great city of Baia.

The bay and city of Baiae. By J. M. W. Turner - The Yorck Project: 10.000 Meisterwerke der Malerei. DVD-ROM, 2002. ISBN 3936122202. Distributed by DIRECTMEDIA Publishing GmbH., Public Domain, https://commons.wikimedia.org/w/index.php?curid=159741

The bay and city of Baiae. By J. M. W. Turner – The Yorck Project: 10.000 Meisterwerke der Malerei. DVD-ROM, 2002. ISBN 3936122202. Distributed by DIRECTMEDIA Publishing GmbH., Public Domain, https://commons.wikimedia.org/w/index.php?curid=159741

Paget’s discovery in 1962 and his conclusions about the tunnel at Baiae are chronicled in his books which I don’t have at hand. But an informative (though slow-loading) website, OracleoftheDead, describes the tunnels, their re-discovery, and the most current exploration in detail. According to Dash, A. Maiuri also discovered the overgrown Baiae tunnel entrance in the 1950s among the ruins of the ancient spa that existed in the town. At that time, the narrow passage was too hot and dangerous to enter.

antrum-entrancePaget assembled a team to help him. The claustrophobic entrance tunnel is only 21 inches wide, barely enough for one person, and 6 ft high. Walking sideways is preferred so as not to bump along the walls. The single long and “dead straight” passage goes on for about 400 feet (122 m) before making a bend that appeared intended to obscure what sight was beyond. A door likely existed at this “Dividing of the Ways” providing an option to keep going or to enter the Oracle Sanctuary. Paget named the straight tunnel the Great Antrum 270 due to its declination of 270 degrees. Later researchers noted that the tunnel opening may have astronomical alignment. Lamp holds were found niched into the smoothed walls suggesting it was amply lit.

The complex was dug out of a deposit created when a massive amount of pulverized material ejected from an eruption about 39,000 years ago. Still raging hot, the material partially welded under the pressure. I can’t find a detailed geologic map of the deposit but it is described as tuff (or tufa), a poorly sorted mix of pumice bits, glassy ash, and rock fragments, derived from a Plinian-type eruption of great violence. More about the volcanism of the area at the end.

What other features were inside the Baiae tunnels and their particular uses is a matter of debate. Some even call the tunnels a hoax. What makes the complex particularly spectacular is that it culminates in the appearance of a “river”, supposedly representing the Styx. The 6 ft wide, 2 ft deep water way in a 5 ft high excavated area is man-made, fed by two boiling springs discovered by a very intrepid diver. The water is drinkable and Paget reported the levels do not change, therefore it is not dependent upon rainfall, but there are rim marks on the wall that indicate the levels do change. Yet the hydrology is a mystery. It’s difficult to judge the characteristics of the stream since no monitoring over any length of time was done. The design of the tunnels to reach the water course is deliberate but how they knew of the underground water source is unresolved. Some think that a surface cave elsewhere signaled its location. Where the flow ultimate goes is also unknown. Fluorescein dye was used as a tracer with no known springs emitting the trace.

Paget’s idea was that the participant crossed the river of the dead during the ritual. The darkness and drug use may have made the trip down the very small “river” seem more dramatic. On the other side was an exit tunnel, created with precision engineering design, that led back to the Oracle sanctuary. One area had been blocked up with material that Paget thought must have been carried back into the tunnel system, possibly by the Romans at a later date. It was also assumed that some ventilation system was used to keep the foul air moving out and fresh air in. Or, it was designed to exaggerate the effect of smoky vapors in certain areas. Robert Temple, a later explorer, reports that the heat and air quality was not bad but one did get low in oxygen in the farthest reaches.  Temple received permission to re-enter the tunnels long after Paget and when they had mostly been forgotten. He produced a book and documentary for National Geographic (2001). He commented on the Smithsonian piece:

It took me 20 years to get permission from the archaeological authorities to undertake the investigations and to film the site, because they believed it to be full of poison gas. But it is not full of poison gas, and the oxygen cylinders and other such precautions which I brought on the first occasion proved to be unnecessary, as well as the rope tied around my ankle so that they could pull out my corpse (I had already signed a form stating that the Italian Government was not responsible for my death). If anyone wants to fund the clearance so that the tunnels may be more fully investigated, let me know.

Temple also says no Italian archaeologists were willing to go with him into the cave, but more work certainly needs to be done. He states there are additional passes to be uncovered and cleared because, he suggests, soil and rubble were placed by the Romans to block them and ‘decommission’ the Oracle. Additional work is required by qualified archaeologists into the tunnels at Baiae to document them more carefully (and officially), discern best when and why they were constructed, how and by whom they were maintained, and what purposed they served through their history. We may not ever know much more if the earth gods have anything to say about it and certainly if the observations do not get into the scientific literature.

Sulfur vents are called fumeroles. These give the “burning fields” of Campi Flegrei their name.

Hell just below the surface

The area of Vesuvius and the Phlagraean Fields are part of a very complex and still active volcanic system. Recent research suggests that the deep magma chamber (that is shared by various discrete volcanoes) is getting shallower, meaning the heat can dissipate in less violent ways than blowing a huge chunk of earth into tiny specks of glass, forming searing clouds of white, buoyed by their own hot gasses, and flow faster than sound to bury the surrounding towns. Pompeii, anyone?

With the huge population areas of Pozzuoli and Napoli (2 million) within the danger zones, this is one of the world’s most dangerous volcanic areas. A Plinian-type eruption starts with a big explosion that can send even geologically-small pyroclastic flows and a rain of ash onto towns [3]. It does not take much to cause havoc and death and authorities are very concerned about evacuating everyone threatened. There is no reason to think that the last recorded big eruption (Vesuvius in 1944) means the end to the hazard. It’s a matter of when and where the eruption will manifest. Baia and Pozzuoli have been subject to really nasty seismic movement related to the expanding and contracting ground within the caldera. Called bradyseisms, the land moves meters up and down in a short time. These movements buried the coast of Baia 10 m under water and raised part of Pozzuoli in 1982-1984 damaging 8,000 buildings in the city center and raising the sea bottom by almost 2 m. This area of Italy is now up to a code yellow in warning (green-yellow-orange-red) for activity. Many people living and visiting here are nervous about Vesuvius but fail to grasp the extensive volcanic and associated seismic hazards that can come at any moment without warning. That, dear readers, is truly terrifying. Hellish conditions are around the geologic corner, so visit Italy while you can and enjoy the moment. (Don’t worry, we’ll probably all be dead by the next con-Flegrei-tion anyway.)


The Campanian plain is pockmarked with volcanoes and remnants of eruptions.

I hope you enjoyed this first feature of Spooky Geology where I discussed environmental conditions created by hydrothermal activity in volcanically hot areas that allowed for certain sites to be associated with magic, prophecy, and death. In another post, or more than one, I’m sure, I will address the concepts of portals to the underworld/gates to Hell.


  1. The article from FT346:32-37 is basically a repeat of a piece that appeared in Smithsonian magazine in 2012. That is available here.
  2. H. Sigurdsson (1999), Melting the Earth, p 51.
  3. G.A. Macdonald (1972), Volcanoes. Macdonald attributes the name ‘Plinian’ to Pliny the Elder, but it was Pliny the Younger, his nephew, who wrote about it in great detail. Pliny the Elder died in the eruption.

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