There is nothing remotely Elysian about the Phlegræan Fields; nothing sylvan, nothing green. The Fields, which lie on the north shore of the Bay of Naples, are part of the caldera of a volcano that is the twin of Mount Vesuvius, the destroyer of Pompeii, a few miles to the east. The volcano is still active, but, today, its most obvious feature is this barren, rubble-strewn plateau. Fire bursts from the rocks in places, and clouds of sulphurous gas snake out of vents that lead up from deep underground.
The Fields, in short, are hellish, and it is no surprise that they have always been associated with all manner of strange tales. Most interesting, perhaps, is the myth of the Cumæan sibyl, who took her name from the nearby town of Kyme – Cumæ – a Greek colony that flourished in about 550 B.C., when the Etruscans still held sway much of central Italy and Rome was nothing but a city-state ruled over by a line of tyrannical kings.

Sulphur drifts from a vent on the barren volcanic plateau known as the Phlegraean Fields, a harsh moonscape associated with legends of prophecy.

The sibyl, so the story goes, was a woman named Amalthæa who lurked in a cave on the Phlegræan Fields. She had once been young and beautiful –beautiful enough to attract the attentions of the sun god, Apollo, who offered her one wish in exchange for her virginity. Pointing to a heap of dust, Amalthæa asked for a year of life for each particle in the pile, but (as is usually the way in such old tales) she failed to allow for the vindictiveness of the gods. Ovid, in Metamorphoses, has her lament that “like a fool, I did not ask that all those years should come with ageless youth as well.” Instead, she aged but could not die. Virgil depicted her scribbling predictions of the future on oak leaves that lay scattered about the entrance to her cave, and states that the cave itself concealed an entrance to the underworld.
The best known – and from our perspective the most interesting – of all the tales associated with the sibyl is supposed to date to the reign of Tarquinius Superbus – Tarquin the Proud. He was the last of the mythic kings of Rome, and some historians, at least, concede that he really did live and rule in the 6th century B.C. According to legend, the sibyl travelled to Tarquin’s palace bearing nine books of prophecy that set out the future of Rome. She offered the set to the king for a price so enormous that he summarily declined – at which the prophetess went away, burned the first three of the books, and returned, offering the remaining six to Tarquin at the same price. Once again, the king refused, though less arrogantly this time, and the sibyl burned three more of the precious volumes. The third time she approached the king, he thought it wise to accede to her demands. Rome purchased the three remaining books of prophecy at the original steep price.

A Renaissance-era depiction of a young Cumæan sibyl by Andrea del Catagno. The painting can be seen in the Uffizi Gallery.

What makes this story of interest to historians as well as folklorists is that there is good evidence that three Greek scrolls, known collectively as the Sibylline Books, really were kept, closely guarded, for hundreds of years after the time of Tarquin the Proud. Secreted in a stone chest in a vault beneath the Temple of Jupiter, the scrolls were brought out at times of crisis and used, not as a detailed guide to the future of Rome, but as a manual that set out the rituals required to avert looming disasters. They served the Republic well until the temple burned down in 83 B.C., and so vital were they thought to be that huge efforts were made to reassemble the lost prophecies by sending envoys to all the great towns of the known world to look for fragments that might have come from the same source. These reassembled prophecies were pressed back into service and not finally destroyed until 405, when they are thought to have been burned by a powerful general by the name of Flavius Stilicho.
The existence of the Sibylline Books certainly suggests that Rome took the legend of the Cumæan sibyl seriously, and indeed the geographer Strabo, writing at about the time of Christ, clearly states that there actually was “an Oracle of the Dead” somewhere in the Phlegræan Fields – a statement that implies, in turn, that the Romans believed an entrance to the underworld existed somewhere on the plateau. So it is scarcely surprising that archaeologists and scholars of romantic bent have from time to time gone in search of a cave or tunnel that might be identified as the real home of a real sibyl – nor that some have hoped that they would discover an entrance, if not to Hades, then at least to some spectacular subterranean caverns.
Several spots have been identified as the antro della sibilla – the cave of the sibyl – over the years. None, though, led to anywhere that might reasonably be thought to be an entrance to the underworld. Because of this, the quest continued, and gradually the remaining searchers focused their attentions on the old Roman resort of Baia, which lies on the Bay of Naples at a spot where the Phlegræan Fields vanish beneath the Tyrrhenian Sea. Two thousand years ago, Baia was a flourishing spa, noted both for its mineral cures and for the scandalous immorality that flourished there. Today, it is little more than a collection of picturesque ruins – but it was there, in the 1950s, that the Italian archaeologist Amedeo Maiuri discovered the entrance to a hitherto unknown antrum. It had been concealed for centuries beneath dense undergrowth sprouting from a vineyard; Maiuri’s workers had to clear a 15-foot-thick accumulation of earth and vines to lay it bare.

The entrance to the Great Antrum – an easily-missed sliver in the midst of a larger Graeco-Roman temple complex. Image: oracleofthedead.com

The antrum at Baia proved difficult to explore. A sliver of tunnel, obviously ancient and manmade, disappeared into a hillside close to the ruins of what may be a Greek temple. The first curious onlookers who pressed their heads into its cramped entrance discovered a pitch-black passageway that was uncomfortably hot and – so Maiuri reported – wreathed in fumes; they penetrated only a few feet into the interior before beating a hasty retreat. There the mystery rested, and it was not revived until the site came to the attention of Ferrand Paget – who liked everyone to call him “Doc” – in the early 1960s.
Paget was not a proper archaeologist. He was a metallurgical chemist (and nephew to Sidney Paget, the well-known illustrator of Sherlock Holmes) who had retired to the Bay of Naples, and excavated as a hobby. As such, his theories need to be viewed with considerable caution, and it is worth noting that when the academic Papers of the British School at Rome agreed to publish the results of the half-decade that he and an American colleague named Keith Jones spent investigating the tunnels, a firm distinction was drawn between the School’s endorsement of Paget’s plans of the interior and its refusal to pass comment on the theories he had come up with to explain when and why it had been built. These theories eventually made their appearance in book form, but attracted little attention – surprisingly, because the pair claimed to have stumbled across nothing less than a real-life “entrance to the underworld.”
Paget was one of the handful of men who still hoped to locate the “cave of the sibyl” described by Virgil, and it was this obsession that made him willing to risk the inhospitable interior. He and Jones pressed their way though the narrow opening and found themselves inside a cramped tunnel, about six feet [1.8m] tall but a mere 21 inches [53cm] wide. The temperature inside was uncomfortable but bearable, and the two men pressed on into a passage that, they claimed, had probably not been entered for 2,000 years.

An overview of the tunnel system at Baia – 3D modelling by John Smout of the Oracle of the Dead site. Reproduced with permission and thanks.

It took Paget and Jones, working in difficult conditions, some time to explore what turned out to be a highly ambitious tunnel system. The interior included an oddly complex network of narrow passageways, the entrances to some of which proved to be blocked up or disguised, and whose precise purchase Paget could only guess at. It is fair to say that most of those who have come after him have admitted themselves more or less baffled by at least some of the odder aspects of the tunnels.
The first of these peculiar features occurred about 400 feet [125m] from the entrance, at a spot where the path diverged, only to merge again some 330 feet [100m] further into the complex. Paget suggested that this “dividing of the ways” had at one time been masked by a wooden door. Swung closed, this would have masked one route to the lower levels. But, opened, it could have been used (so the explorer suggested) as a ventilation system; hot, vitiated air would be sucked out of the tunnel complex at ceiling level, while currents of cooler air from the surface were constantly drawn in along the floor.

“Doc” Paget’s plan of Baia’s mysterious “Oracle of the Dead” shows the complex layout of the tunnels and their depth below ground level – though more recent reconstructions reveal some errors. Click to view in higher resolution.

As Paget and Jones went deeper into the hillside, two further puzzles revealed themselves. First, at the bottom of a much steeper passage, some 650 feet [200m] inside the tunnel, they discovered an underground stream 6 feet [1.8m] wide, which disappeared into the darkness. The river itself was hot to the touch. Fording it and ascending a steep passageway on the far bank, the men next came upon what they thought had been an “inner sanctuary.” What this room was, or had been used for, remains a mystery; at some point in the tunnels’ history, it had been laboriously filled in, and it has never been excavated. Further blockages were found elsewhere in the tunnel system; according to Paget’s rough calculations, something like 7,000 cubic feet [200m³] of soil had been carried in baskets from the surface, an operation that would have required 15,000 man-journeys down the narrow passageways. Somebody, he decided, had once been very anxious to stop up the tunnel system and conceal its purpose.
So what was the “Great Antrum,” as Paget called it? Who had built it – and what had it been used for? And who had blocked access to it? In time, “Doc” came up answers to all of those questions.

The Phlegræan Fields (left) and Mount Vesuvius, after Scipione Breislak’s map of 1801. Baiae lies at the northeastern tip of the peninsula of Bacoli, at the extreme westerly end of the Fields.

The tunnel system, he proposed, had been constructed by priests to mimic a visit to the Greeks’ mythical underworld. In this interpretation, the underground stream represented the fabled River Styx, which the dead had to cross to enter Hades; a coracle, Paget speculated, would have been waiting to ferry visitors across, and a crossing made in darkness might have concealed the stream’s meagre breadth. On the far side, initiates would have ascended to the hidden sanctuary, and it was there they would have met… whom? One possibility, “Doc” thought, was a priestess posing as a sibyl, and dispensing prophecies for a steep fee. For this reason he took to calling the complex the “Antrum of Initiation.”
The tunnels, then, in Paget’s view, might have been constructed to allow priests to persuade their patrons – or perhaps simply wealthy travellers – that they had journeyed to the underworld. The heightened temperatures below ground, combined, perhaps, with drifts of volcanic vapour, could certainly have given that impression. And if visitors were scared, befuddled, or even drugged, it would have been possible to create a powerfully otherworldly experience, one capable of persuading even the most sceptical of the priests’ power.

The Great Antrum is now lined with Roman-era cocciopesto waterproof cement. Image: oracleofthedead.com.

In favour of this argument, “Doc” supposed, was the careful planning of the tunnels. He pointed to the huge number of lamp niches which had been built into the tunnel walls; there are more than 550 in all, and they come at the rate of one every three feet [0.9m] in the lower levels, far more than would have been required merely to provide illumination. This feature made no sense if the tunnels were (as more mainstream archaeologists have always suggested) merely devised to channel warm air to Baia’s famous Roman baths above. And the “dividing of the ways,” with its hidden door, would have allowed a party of priests – and the “sibyl,” too, perhaps – quick access to the hidden sanctuary.
Indeed, the whole system, Paget thought, closely matched ancient myths of visits to the underworld. In Virgil’s Aeniad, for instance, the hero, Aeneas, crosses the Styx only once on his journey underground, emerging from Hades by an alternate route. The discovery of a further, blocked, tunnel at the back of the hill suggests that the complex at Baia may have been constructed to allow just such a journey. And since Virgil himself, in Paget’s argument, had lived nearby, he might himself have been initiated into Baia’s mysteries.

The underground stream that Paget dubbed the “River Styx.” The water level is significantly lower now than it was in the 1960s, and the bed of the stream has been choked with rubble dumped there by successive investigators. Image: oracleofthedead.com

Dating the construction of the complex was a greater challenge. The explorers found little evidence inside the tunnels to point to the identity of the builders – just a mason’s plumb bob in one niche, and some ancient graffiti, which can be read as a date: “IIII KAL MAR,” or 26 February, in an unknown year. But, working on the assumption that the passages had once formed part of the surrounding temple complex, they concluded that they could best be dated to the late archaic period, around 550 B.C. – at pretty much the time, that is, that the Cumæan sibyl was said to have lived. If so (and Italian archaeologists prefer to believe that the tunnels are later, and Roman) then the complex was almost certainly the work of the Greek colonists of Cumæ itself. As for when the tunnels were blocked up, that – wrote Paget – must have taken place after Virgil’s time, during the early Imperial period of Roman history. But who exactly ordered the work, or why, he could not say.
In time, Paget and Jones resolved at least one of the Great Antrum’s mysteries. In 1965 they persuaded a friend, Colonel David Lewis of the U.S. Army, to investigate the Styx for them using scuba apparatus. Lewis and his son dived into the stream and followed it into a tunnel that dramatically deepened, discovering an underwater cave, along with the source of the stream’s warmth: two springs of boiling water, superheated by the volcanic chambers of the Phlegræan Fields. The Styx, Lewis reported, is fed by two narrow entrances to the left of it, now submerged. These entrances are hand cut, and a man can just squeeze through. Lewis also found a tunnel leading up to Paget’s “sanctuary” from the back end of the Styx. It remains blocked with soil and has not been properly explored by anyone.

One of the two boiling springs that feed the “Styx,” photographed in 1965, 250 feet beneath the surface, by Colonel David Lewis, U.S. Army.

Whether Paget’s elaborate theories are correct remains a matter of debate. It seems much more likely than not that the tunnel complex served some ritual purpose; in addition to the mute evidence of the lamp niches, the recent efforts of another British researcher, John Smout, have established that the entrance passageway was angled so that it would have been picked out and illuminated by the sunrise over Mount Vesuvius at each equinox around 500 B.C. One central question may well be whether it is possible to see Paget’s channel of “boiling water” deep underground as anything other than a deliberate representation of one of the fabled rivers that girdled Hades – if not the Styx itself, then perhaps the Phlegethon, the mythic “river of fire” that, in Dante’s Inferno, boils the souls of the departed. And for all the scepticism of the archaeologists, historians of the ancient world do not dispute that the powerful priests of antiquity were perfectly capable of mounting elaborate deceptions. A recent geological report on the far better known Greek oracle site at Delphi demonstrated that fissures in the rocks nearby brought intoxicating and anaesthetic gases to the surface at the spot, suggesting that it may have been selected and used for a purpose much like the one Paget proposed at Baia.
Yet much remains mysterious about the Great Antrum – its purpose, its still hidden exits, and, not least, the vexed question of how its ancient builders, working with primitive tools at the end of the Bronze Age, could even have known of the existence of the “River Styx,” much less excavated a tunnel that so neatly intercepted it. There is no trace of the river at the surface – and we still have no real idea where its source is, or where it leads.

A side view of the Oracle tunnel complex. 3D mapping by oracleofthedead.com.

Little seems to have changed at Baia since Paget’s day. His discoveries have made remarkably little impact on tourism at the ancient resort, and his willingness to embroider evidence (and, at least occasionally, to just make it up) means that work still needs to be done to unpick fact from fiction in the Great Antrum. Today the network of passages is locked up, infested with scorpions, and dangerous to enter. Little attempt is made to exploit the idea that the narrow entrance in the rock was once thought to be an entrance to the Roman’s hell – and, pending proper investigation by archaeologists, not much more can be said about the tunnels’ origin and purpose. But among the many mysteries of the ancient world, the Antrum on the Bay of Naples remains among the most intriguing.
Thanks
My thanks to John Smout and Peter Knight for several illuminating discussions regarding the Oracle site and Doc Paget’s claims. For full details of the tunnel complex, and to keep up to date with ongoing research at Baia, visit oracleofthedead.com. 

Tunnels inexplicably divide within the Great Antrum. Image: oracleofthedead.com.

Sources
C.F. Hardie. “The Great Antrum at Baiæ.” Papers of the British School at Rome 37 (1969); Victor Failmezger. Paget, Discoverer of Hades. Front Royal [VA]: National Media Services, 2013; A.G. McKay. Cumæ and the Phlegræan Fields. Hamilton [Ont]: Cromlech Press, 1972; Daniel Ogden. Magic, Witchcraft and Ghosts in the Greek and Roman Worlds: A Sourcebook. Oxford: Oxford University Press, 2002; R.F. Paget. “The ‘Great Antrum’ at Baiæ: a Preliminary Report. Papers of the British School at Rome 35 (1967); R.F. Paget. In the Footsteps of Orpheus. London: Robert Hale, 1967; H.W. Parke. Sibyls and Sibylline Prophecy in Classical Antiquity. London: Routledge, 1988; P.B. Wale. “A conversation for ‘The Antrum of Initiation, Baia. Italy’.” BBC h2g2, accessed 12 August 2012; Fikrut Yegul. “The Thermo-Mineral Complex at Baiæ and De Balneis Puteolanis.” The Art Bulletin 78:1, March 1996.