contact: Jeff Matthews

Caves & Tunnels & Holes in the Ground

Honeycombing —and undermining — the hill upon which much of Naples sits are hundreds of caves like the one seen here along the Corso Vittorio Emanuele.

Some time ago I went to a restaurant at the tiny Piazzetta Leone a Mergellina, just a block from the small Mergellina harbor. Inside, I asked for the men’s room and followed directions the way one does —right in there, around there, back through there. I wound up in a cave, a real cave. It must have extended 50 yards back from the main restaurant; it was quite high and all dug out of the hill that separates Mergellina from Fuorigrotta. The cave was nicely fitted out with the necessary wherewithal to keep a restaurant going: refrigerators, air-conditioning units, storage racks, etc. And the men’s room, of course. There were no bats, at least none that I noticed.

As it turns out, the restaurant is only a few yards from the 700–meter Roman tunnel (popularly called “The Neapolitan Crypt”) connecting Naples with the area beyond that mountain, specifically, the area of Fuorigrotta, the important Roman city of Pozzuoli, and the Imperial port of Baia. It was built by Lucius Cocceius Auctus, one of the great architects in the age of Augustus Caesar. He also built the other tunnel, the Seiano Grotto, two miles up from Mergellina, which burrowed beneath the Posillipo hill for half a mile. He built another tunnel at Baia, itself, to join the port facilities to Lake Averno. A busy man, Cocceius. Roman tunnels, of course, no longer carry traffic, though the Fuorigrotta one was used much later than one might think. It was actually kept up and expanded by the Spanish and then the Bourbons in the 1700s. Coach traffic passed through it well into the 1800s.

In 1882-5 and 1925, two modern tunnels, the "Nuova Galleria Posillpo" and the “Laziale”, respectively, were built to join Mergellina with the north. They flank the “Neapolitan Crypt” on either side and are heavily used today. (The older one, the "Nuova Galleria Posillpo", also known originally as the Municipal Tramway Tunnel, was renamed "Quattro Giornate" ("Four Days) in honor of this WWII episode.) The "Laziale" (today,generally called, simply, the Posillipo Tunnel) was so called from the adjective for "Lazio," the region (state, this context) is Rome is the capital of. Both tunnels have over the years served both tram and car traffic. The tunnel essentially had the same function as the old Seiano one, to get traffic out of Naples and up the coast towards Rome. Back in the main part of Naples, there is now also the Galleria della Vittoria (Victory Tunnel), built in 1927–8; it tunnel joins the center of Naples to the areas of Chiaia and Mergellina by running  from the main port beneath Monte Echia (or Pizzofalcone), the cliff that overlooks Santa Lucia and the Castel dell’Ovo (the “Egg Castle”).

Readers should note the problems connected with building these tunnels. Most of the difficulty has to do with the changing nature of the subsoil as you dig through. Going from Mergellina to Fuorigrotta, for example, you are tunneling through tuff rock laid down by separate volcanic eruptions eons ago, producing qualitatively different kinds of material. That left engineers puzzled on various occasions; they were getting cave-ins where there should have been none. For example, the Municipal Tramway Tunnel, mentioned above, was indeed opened in 1885, but it had to be closed for an extended period in 1890 because of cave-ins. The other tunnel mentioned above, the Laziale, although finished in 1925 had shown numerous incidents of earth movement and crumbling during construction and then showed additional damage in 1932. The Diretissima Naples-Rome train tunnel that runs the length of the city and then beneath the Posillipo hill was first tested in 1917; it had problems and was closed in 1922 and was under repairs until 1925. It had more problems in the 1930s.

Most recently, opened about 20 years ago, are the two major tunnels in the city (each about 1 km long) that form part of the “Tangenziale”, the by-pass highway that links Naples with the main Italian autostrada network. One passes directly beneath the Capodimonte hill and the other beneath Vomero. There is a third tunnel as the road moves out of the main city into the area known as the Campi Flegrei.


Tunnels are just the start when you talk about “underground Naples”. Sixty percent of the city, as they say, “rests on nothing”. Besides ancient tunnels, aqueducts, cisterns, and catacombs,  there are hundreds (!) of quarried sites in Naples —man-made caves. They have been dug out of the hills of the city in the course of the centuries, going back to the Greeks, who quarried the stone to build the original city. Expansion of the city and of the city walls continued to about the time of the fall of the Roman Empire in the 5th century. Extensive rebuilding and expansion picked up eight centuries later under the Angevin rule in Naples, truly exploded under the Spanish and continued well into the 1700s.

The ex-quarries may be just a few cubic meters in volume, maybe serving as someone’s garage or storage shed today, or they can be truly mammoth. For example, the Spanish dug into the hill in the Chiaia section of town to build the Palazzo Cellamare (also Cellammare) in the 1560s. That man–made cavern has found various uses through the centuries and, today, has been expanded even further and converted into an underground seven-screen cinema. Even larger is the space now occupied by the Augusteo cinema. The entrance is at the bottom station of the main cable-car on via Toledo, downtown, almost at the Royal Palace. It covers an underground area of more than two square miles, and served as an air–raid shelter in WW2, holding 15,000 persons. Speaking of cable-cars, there are four of them in Naples, each with its own tunnel to get from sea-level up to the Vomero and Posillipo sections of town at around 500 feet; some of the time they run under open sky, but most of the time they pass right beneath people’s homes.



Also, the Bourbons dug out an enormous cave beneath the Capodimonte palace in the 1700s. Later, the same dynasty in the 1800s built a large underground passageway from the Royal Palace downtown along the port and under Monte Echia to the then new barracks at Chiaia. It is said to have been for the dual purpose of moving troops into the palace area and/or moving the royal family out in case of trouble. There are two older underground railway lines beneath Naples, with one new one under construction. That makes three separate railways beneath the city with a total number of 15 underground stations plus more on the way. Some of the stations are very deep. The deepest and most difficult ones to build were the ones on the Vomero hill. It took almost 20 years to finish them; now there is another underground train line coming in from the new university and the San Paolo football stadium in Fuorigrotta. That’s another major tunnel and four or five stations.

[see related entries on the metropolitana train lines]

I have barely scratched the surface. (Sorry. You knew that one was coming!) There is also some archaeological excavation in downtown Naples. Much of the historic center of the city actually rests 40 feet above the original Greco-Roman city, which was covered by a great mudslide in the sixth century. The excavations to open the Roman market beneath San Lorenzo took 25 years.

Not surprisingly, in the course of the centuries, some mythology has attached itself to the gigantic caves and tunnels of Naples. The average person in southern Italy during the so-called “Dark Ages”, centuries before the Renaissance, knew little about his Roman forebears and absolutely nothing about the ancient Greeks. Who could have hollowed out all the hillsides to produce the caves? In one example, the Roman poet Virgil was held in such high esteem in the Middle Ages that he was reputed to have conjured the “Neapolitan Crypt” into existence a thousand years earlier by his magical powers. Or, another possibility, perhaps it was the Cimmerians (as in “Cimmerian darkness”), the mythological race that Homer places near Hades in an abode of “eternal gloom”. The Greek historian, Strabo, as well as Roman writers such as Cicero and Pliny the Elder, place this race of giants near Cuma, near Naples, and tell of them carving their dwellings out of the hills in order to hide from the light.

Finally, in spite of engineers’ claims that much modern construction actually reinforces the ground we live on, people around here get worried whenever it rains a lot, as it has this week. Cave–ins and landslides are always to be feared in Naples; there is a separate entry about those phenomena: Cave-ins & sink-holes & siphons.

(all of the images, above, are from the streets of urban Naples)                                   
                                        

============================added May 19, 2023 =============================

ISPRA is the Italian acronym for Italian Institute for Environmental Protection and Research, one section of which deals with "hydrogeological instability" --roughly "what happens when you get too much much rain." How much is too much? Normally, I have no problem with the metric system. Although I grew up with the English system, I understand kilometers, but my brain freezes at, say, 250 mm (millimeters) of rain. I look it up and it says "1 inch" and I think, "Solid rain." Then I read "per hour" and I remember that personally in Hawaii. It rained for 9 hours like that and floated cars in the university parking lot. Fine, it was a rough day, but still... Then I see that in Ravenna a few days ago,

"More than 20 rivers burst their banks, leaving 13 people dead and forcing thousands from their homes after six months' rainfall fell in a day and a half. More bodies were found on Thursday after almost every river flooded between Bologna and the north-east coast 115km (70 miles) away Some 280 landslides have taken place.".

Like everyone else in Italy, I look out and up and wonder, how are we doing here? Today I see  the sun. Good, I'm safe. That's short-sighted of me. Behind me, there is a large constructed wall holding back a high "overburden" —a legitimate engineering term—of dirt, vegetation and two multi-story houses.

This next paragraph is from a 1967 book, The Subsoil of Naples, that I translated into English for the city in the 1990s:

"Movement of varying degrees in and on the subsoil  —from simple cracks in buildings to full-scale collapses of buildings and retaining structures and the opening of sink-holes in the streets— are unfortunately not a new phenomenon for the city of Naples. They have increased over time and affected most areas of the city, becoming a plague that afflicts the city and a cause for justified concern and alarm on the part of the public. We have to interpret the causes correctly. We have to examine the evolution of soil movement over the years and see if and how it is different from one zone of the city to another." The few images below are all from local landslides or sink-holes in urban Naples, the streets."

(the entire book is at the links directly below)

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See the Underground Portal for related entries, particularly "The Subsoil of Naples", a 1967 book commissioned by the city of Naples and, in that work, Chapter 9, for a discussion of what can happen when the city "rests on nothing."
            
  also see the portal for architecture and urban planning       to top of this page