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 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.

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 Tarqinius 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.

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 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 an 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