Baiæ (Italie): The Unsolved Mystery of the Tunnels


It took Paget and Jones, working in difficult conditions with a small group of volunteers, the beter part of a decade to clear and explore what turned out to be a highly ambitious tunnel system. Its ceremonial function seemed to be confirmed by the existence of huge numbers of niches for oil lamps–they occurred every yard in the tunnels’ lower levels, far more frequently than would have been required merely to provide illumination. The builders had also given great thought to the layout of the complex, which seemed to have been designed to conceal its mysteries.


The “River Styx”–an underground stream, heated almost to boiling point in places, which runs through at the deepest portions of the tunnel complex. It was the discovery of this stream that led Paget to formulate his daring hypothesis that the Great Antrum was intended as a representation of the mythic underground passageways to Hades.

Within the portion of the tunnels choked by rubble, Paget and Jones found, hidden behind an S-bend, a second blockage. This, the explorers discovered, marked the place where two tunnels diverged. Basing his thinking on the remains of some ancient pivots, Paget suggested that the spot had at one time harbored a concealed door. Swung closed, this would have masked the entrance to a second tunnel that acted as a short-cut to the lower levels. Opened partially, it could have been used (the explorer suggested) as a remarkably effective 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.

But only when the men went deeper into the hillside did the greatest mystery of the tunnels revealed itself. There, hidden at the bottom of a much steeper passage, and behind a second S-bend that prevented anyone approaching from seeing it until the final moment, ran an underground stream. A small “landing stage” projected out into the sulfurous waters, which ran from left to right across the tunnel and disappeared into the darkness. And the river itself was hot to the touch–in places it approached boiling point.

Conditions at this low point in the tunnel complex certainly were stygian. The temperature had risen to 120 degrees Fahrenheit; the air stank of sulfur. It was a relief to force a way across the stream and up a steep ascending passage on the other side, which eventually opened into an antechamber, oriented this time to the helical sunset, that Paget dubbed the “hidden sanctuary.” From there, more hidden staircases ascended to the surface to emerge behind the ruins of water tanks that had fed the spas at the ancient temple complex.


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.

What was this “Great Antrum,” as Paget dubbed it? Who had built it–and for what purpose? And who had stopped it up? After a decade of exploration, he and Jones had formulated answers to those questions.

The tunnel system, the two men proposed, had been constructed by priests to mimic a visit to the Greeks’ mythical underworld. In this interpretation, the stream represented the fabled River Styx, which the dead had to cross to enter Hades; a small boat, the explorers speculated, would have been waiting at the landing stage to ferry visitors across. On the far side these initiates would have climbed the stairs to the hidden sanctuary, and it was there they would have met… who? One possibility, Paget thought, was a priestess posing as the Cumæan sibyl, and 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 travelers–that they had traveled through the underworld. The scorching temperatures below ground and the thick drifts of volcanic vapor would certainly have given that impression. And if visitors were tired, befuddled or perhaps simply drugged, it would have been possible to create a powerfully otherworldly experience capable of persuading even the skeptical.


A general plan of the tunnel complex, drawn by Robin Paget. 

In favor of this argument, Paget went on, was the careful planning of the tunnels. The “dividing of the ways,” with its hidden door, would have allowed a party of priests–and the “Cumæan sibyl” too, perhaps–quick access to the hidden sanctuary, and the encounter with the “River Styx” would have been enhanced by the way the tunnels’ S-bend construction concealed its presence from new initiates. The system, furthermore, closely matched ancient myths relating 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 tunnel complex at Baiæ seemed to have been constructed to allow just such a journey–and Virgil, in Paget’s argument, had lived nearby and might himself have been an initiate in Baiæ’s mysteries.

Dating the construction of the complex was a greater challenge. The explorers found little evidence inside the tunnels that might point to the identity of the builders–just a mason’s plumb bob in one of the niches and some ancient graffiti. But, working on the assumption that the passages had 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, the complex was was almost certainly the work of the Greek colonists of Cumæ itself. As for when the tunnels had been blocked up, that–Paget thought–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 solved at least some of the Great Antrum’s mysteries. In 1965 they persuaded a friend, Colonel David Lewis of the U.S. Army, and his son to investigate the Styx for them using scuba apparatus. The two divers followed the stream into a tunnel that dramatically deepened and discovered the source of its mysterious heat: two springs of boiling water, superheated by the volcanic chambers of the Phlegræan Fields.

Whether Paget and Jones’s elaborate theories are correct remains a matter of debate. That the tunnel complex served some ritual purpose can hardly be doubted if the explorers’ compass bearings are correct, and the specifics of its remarkable construction seem to support much of what Paget says; the alternative explanation–that the tunnel was dug by the Roman army and once lead to a subterranean restaurant–seems to be considerably more far fetched. In particular, it is hard to see the 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. Historians of the ancient world do not dispute that powerful priests were fully capable of mounting elaborate deceptions–and 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 that spot, suggesting that it may have been selected and used for a purpose much like the one Paget proposed at Baiæ.

Yet much remains mysterious about the Great Antrum–not least the vexed question of how ancient builders, working with primitive tools at the end of the Bronze Age, could possibly 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 boiling river at the surface–and it was not until the 1970s, after Paget’s death, that his collaborators finally discovered, by injecting colored dyes into its waters, that it flows into the sea miles away, on the northern side of Cape Miseno.


Paget found one foot-high fragment of roughly painted graffiti close to the entrance of the tunnels. He interpreted the first line to read “Illius” (“of that”), and the second as a shorthand symbol representing a prayer to the Greek goddess Hera.

Little seems to have changed at Baiæ since Paget’s day. His discoveries have made remarkably little impact on tourism at the ancient resort, and even today the network of passages he worked so long to clear remain locked and barely visited. A local guide can be hired, but the complex remains difficult, hot and uncomfortable to visit. Little attempt is made to exploit the idea that it was once thought to be an entrance to the underworld, and, pending reinvestigation by trained archaeologists, not much more can be said about the tunnels’ origin and purpose. But even among the many mysteries of the ancient world, the Great Antrum on the Bay of Naples surely remains among the most intriguing.

C.F. Hardie. “The Great Antrum at Baiae.” Papers of the British School at Rome 37 (1969); Peter James and Nick Thorpe. Ancient Inventions. London: Michael O’Mara, 1995; A.G. McKay. Cumae and the Phlegraean 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 Baiae: a Preliminary Report. Papers of the British School at Rome 35 (1967); R.F. Paget. In the Footsteps of Orpheus: The Story of the Finding and Identifications of the Lost Entrance to Hades, the Oracle of the Dead, the River Styx and the Infernal Regions of the Greeks. 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 Baiae and De Balneis Puteolanis.” The Art Bulletin 78:1, March 1996.