Cumae was an important early Greek colony on the Bay of Naples, but was destroyed in the thirteenth century AD and remains a remote and overgrown place. The Sibyl’s ‘cave’ – first identified in 1932 – is a trapezoidal corridor, or dromos, hewn out of the rock, some 44 metres long, 2.5 metres wide and 5 metres high. At one end is an oecus , an inner sanctum, and on either side are openings, some leading to chambers that may have contained lustral waters. This seems likely to be where the Roman poet Virgil – buried somewhere nearby – had his Trojan hero Aeneas visit the Sibyl on his way to found Rome (Aeneid vi, 42-51). The image in the Prologue draws on the account of Virgil, who describes prophecies written on oak leaves, and the Roman poet Ovid, who recounts the story of Apollo condemning the Sibyl to wither away for as many years as she could hold grains of sand ( Metamorphoses 14). The use of opium is conjectural, but seems consistent with the trance-like state of the oracle, as well as the pliability she may have wished of her supplicants. The Sibyl is said to have sold a book of prophecies to the last king of Rome, Tarquinus Superbus, in the fifth century BC, and these were consulted as late as the fourth century AD. The cult was important in the ideology of the first emperor, Augustus, and it is possible that he and subsequent emperors secretly visited the Sibyl in her cave.
The Temple of Jupiter at Cumae was transformed into a Christian basilica in the fifth-sixth century AD, and the cave of the Sibyl shows evidence for Christian occupation and burials. An association between Sibylline prophecy and early Christianity has long been proposed on the basis of Virgil’s fourth Eclogue, where he has the Sibyl foretelling a future ‘golden age’, heralded by the birth of a boy; it is also seen in the medieval Des Irae, which has no known ancient source but may derive from this tradition.
The final resting place of St Paul may be Rome, where a fourth-century sarcophagus found in 2006 beneath the Church of St Paulo fuori le Mura has been associated with him. The tradition that he was martyred along with St Peter in the Circus of Caligula and Nero, the site of Piazza San Pietro in the Vatican, led me to imagine that his original tomb may lie under St Peter’s Basilica, close to the tomb identified as that of St Peter. The extension in this novel to the ancient necropolis excavated during the 1940s under St Peter’s is fictional, but its early Christian burials, symbols and inscriptions are based on actual catacombs I have explored elsewhere in Rome and in North Africa.
The shipwreck off Sicily is based on a wreck of about AD 200 excavated under my direction at Plemmirio, off Capo Murro di Porco south of Siracusa. This was where the British Special Raiding Squadron landed in July 1943, in advance of the disastrous glider assault recounted in this novel; my grandfather Captain Lawrance Wilfrid Gibbins gave me a first-hand account of this action, as he was close inshore that day with his ship Empire Elaine of the assault convoy. The seabed around the Roman wreck was strewn with ammunition, thrown into the sea after the Italian garrison surrendered. We had been led to the site by an account of one of Captain Cousteau’s divers, who had seen the wreck in 1953 during a Calypso expedition. The description of the site is largely factual up to the point where Jack and Costas follow the shotline beyond fifty metres depth. Nevertheless, the deep wreck they discover, with Italian wine amphoras from the first century AD, is itself closely based on other sites I have seen, with the same form of wine amphora found in the taverns of Herculaneum and Pompeii. One of those wrecks, off Port-Vendres in the south of France, is dated to the reign of Claudius by the stamped inscriptions on lead ingots in the cargo. The ingots of Narcissus are fictional, but the inscription is closely based on the actual formulae found on British lead-silver ingots of this period, some of which have also been found at Pompeii.
One of our finds from the wreck was an amphora sherd with the painted graffito Egttere, meaning ‘to go’. Other finds included a sounding lead with a cross-shaped depression underneath, as described in the novel, and – uniquely from a wreck – a Roman surgeon’s instrument kit.
Another Roman wreck, off Italy, has produced the contents of an apothecary’s chest – numerous small boxwood phials filled with substances including cinnamon and vanilla. So far, nobody has identified opium from an ancient shipwreck, though its use is well established in the ancient sources. Pliny the Elder devotes a chapter to the poppy and its sleep-inducing extracts, telling us that ‘the seed cures leprosy’, and describes the overdose taken by the father of one Publius Licinius Caecina, a man of praetorian rank, who ‘died of opium poisoning at Bavila, in Spain, where an unbearable illness made his life not worth living’ (Natural History xx, 198-200).
We searched for an ancient Greek wreck also reported by Cousteau’s divers, in deep water beyond the Roman wreck. On our last dive we discovered a scatter of amphoras, several of seventh or sixth century BC date. At this point the sea bed dropped off to abyssal depth, three thousand metres and more, and we could only imagine what treasures lay in the darkness beyond. You can see a picture of me holding one of those amphoras at the moment of discovery on my website.
In 2007 archaeologists announced a stunning discovery in the heart of ancient Rome. Probing beneath the Palatine Hill – home of the emperors, and site of Rome’s earliest settlement – revealed a subterranean chamber, some 16 metres below the House of Augustus. The chamber measures seven and a half metres high and six metres wide, and was formed partly from one of the natural fissures that honeycomb the hill. A camera lowered into the grotto revealed lavish mosaics studded with seashells, and in the centre of the floor a marble mosaic of a white eagle, an imperial motif. This may be the long-lost Lupercale, the cave where Rome’s founders Romulus and Remus were supposed to have been suckled by the she-wolf, and decorated by Augustus to form the focus of a cult which lasted until Christianity eclipsed the old rituals. Nearby was a circular shrine of Vesta, as described in the novel, part of a cult which survived until the time of the last known Vestal Virgins, Coelia Concordia, in the late fourth century AD.
The ‘urban speleologists’ of my novel are inspired by true-life heroes of underwater archaeology, a group of divers and explorers who have charted the fetid passageways of the Cloaca Maxima – the ‘Great Drain’ – beneath the city of Rome. The main line of the Drain runs from the forum to the river Tiber beneath the Arch of Janus, where another branch runs in from under the Palatine Hill. The entrance beneath the Arch is fictional, though the appearance of the circular staircase is inspired by one that leads into the Aqua Virgo, the aqueduct that feeds the Trevi Fountain. The description of being in the Cloaca and inside an aqueduct is based on my experience and on the accounts of ‘urban speleologists’ who have gone further, revealing many areas under Rome that remain to be explored. The continuation of the tunnel beneath the Palatine is conjectural – the central chamber is based on the appearance of the Cave of the Sibyl at Cumae – though it follows a plausible route between known points of the main drain; the idea that such a project should have been the brainchild of Claudius is consistent with his bent for utilitarian projects, including his aqueduct in Rome, the Aqua Claudia, his huge rock-cut tunnel to drain the Fucine Lake and his construction of the great harbourworks at Ostia, the port of Rome.