The archaeological park is one of the most beautiful places in the city and along the coast of Posillipo. Among the most important sites are the "cave of Sejanus", the underwater park of Gaiola, the imperial villa of Pausilypon (including the
odeon, theatre) and the Palace of the Spirits.
Imperial villa The ruins of the Roman villa of
Vedius Pollio, also known as the Imperial Villa, include a 2000-seat theatre on the rocky promontory at the end of the Bay of Naples. Some of the villa's rooms can be seen with traces of the wall decorations while its marine structures and fish ponds are now part of the neighbouring submerged Gaiola Park. The villa was built in the first century BC by Publius Vedius Pollio. On his death in 15 BC, the villa was bequeathed to
Augustus, and remained in imperial possession for his successors at least until Hadrian, as witnessed by a
stamped water pipe. In various points the presence of water supply pipes (coated with hydraulic mortar) show the opulence of the facilities. The George Vallet Archaeological museum in
Sorrento has a model of the villa.
Tunnel of Sejanus Access for visitors to the ruins of the imperial villa is currently through the Tunnel of Sejanus. The extraordinary 770 metre-long
Grotta di Seiano or "cave of Sejanus" passes beneath the Posillipo hill and connected the imperial villa and other patrician villas nearby with the
Phlegraean Fields and the towns and ports of
Puteoli (
Pozzuoli) and
Cumae. It owes its name to Lucius Aelius Seianus (
Sejanus), prefect of the emperor
Tiberius, who according to tradition commissioned its enlargement in the first century AD; the first tunnel was built 50 years earlier by architect
Cocceius Auctus at the behest of
Agrippa. The eastern entrance is cut into the rock cliff within the archaeological park while the western entrance was a monumental arch with
opus reticulatum lining the cliff sides, and both ends being of about 14 m height. The height, width and length of the tunnel made it a great engineering achievement and an extravagant one considering it served only a small population. An enormous volume of rock alone had to be removed though some served as building material for the villas. The tunnelling was complicated by the alternation of pozzolanic earth with tufa necessitating the elaborate lining of most of the tunnel with stonework of
opus reticulatum and then with vaulting on top of these walls. Work progressed at 5–7 m per day as indicated by the joints between sections. It was not perfectly straight in plan but included small deviations near the centre where the tunnellers from each end met after remarkably small inaccuracies of alignment given the techniques of the time. It had three secondary side tunnels ending in openings overhanging the bay to provide light and ventilation. Although known about by scholars (for example it is referred to in the Polish writer
Adam Mickiewicz's epic
Pan Tadeusz published in 1834), it had fallen into disuse over the centuries. it was rediscovered during works for a new road in 1841 and immediately brought to light and made passable by
Ferdinand II of the Two Sicilies, becoming a tourist destination. Additional lining and arches were built to repair and reinforce the ancient walls. During
World War II, it was used as an
air raid shelter for the inhabitants of
Bagnoli; the war and landslides during the 1950s took it back to a state of neglect since when it was restored.
Other sights The remains of other Roman houses can be seen in Marechiaro along the beach, or at Calata Ponticello where there is an Ionic column base and a brick niche. On the cliff towards Gaiola are the remains of the "House of the Spirits" also called "Villarosa" which was the
nymphaeum of the villa and also built in the first century BC. Further along the coast to the west is the perimeter of the "School of Virgil" where it was believed that the "prophet" practised magical arts. The grandeur and luxury of these villas are documented in the George Vallet Archaeological museum. The
Roman aqueduct supplying the coastal villas was a branch of the Serino aqueduct or
Aqua Augusta and was discovered in 1882 when the Grotta Nuova di Posillipo was made for a tramway through the hill. Ancient inscriptions found inside the tunnel verify that it fed the villa of Felix Pollio, among others, mainly intended for the
nymphaeum and the baths. ==Modern developments==