How does one of the world’s most historic cities build a groundbreaking subway line?Extremely slowly—and with teams of archaeologists standing by.

© David Cicconi Contructio at the Piazza Venezia
| Credit: Contructio at the Piazza Venezia

Scrape by scrape, ancient Rome emerges. At the heart of the city, in pits secured by scaffolding and little wider than railway cars, the modern gives way to the Renaissance. Medieval brick falls away. Sunlight shines on imperial marble. A shovel scratches the ground. The upturned earth, undisturbed for 2,000 years, smells sharp and fresh.

In the Italian capital, where every spade hole has the potential to contain buried treasure, the ancient still governs the modern. Any underground construction project—the laying of a gas line, the expansion of a basement—requires a visit from the city’s archaeologists. So when the city planners decided in 1990 to update their subway system, attempting to plug a glaring gap in one of the least developed underground transit systems in Europe, they expected a challenge.

The new Linea C—construction on the line began in 2007 and is scheduled for completion in 2015—will be the first to service Rome’s historic center and will pass through an area of vital interest to locals, travelers, and archaeologists alike. Plotted to run from the Colosseum to the Forum, it will pitch west at Trajan’s Market and head to the Theater of Pompey, where Julius Caesar recoiled from Brutus’s knife. From there, it will slip under the Tiber River toward Hadrian’s tomb and on to the countryside beyond.

Building the line through one of the world’s most history-rich areas will require feats of technical engineering and planning unheard of in most cities. To pass under the oldest archaeological strata, the metro will have to plunge a full 90 feet below street level, three times deeper than Rome’s existing lines. In the city center, the twin tunnels will also be larger than Rome’s other metro lines, with a diameter of 29 feet instead of the standard 20. The extra width means that if an archaeological discovery—an unexpected temple, say, or an emperor’s villa—blocks a proposed subway entrance, the station (and passenger platform) can easily be shunted down the line. To further avoid damaging archaeological layers (and any resulting controversies), the contractors will have to work like laparoscopic surgeons, minimizing trauma by tunneling through existing ventilation and entrance shafts to build the stations below.

And then there are the considerations for what’s aboveground, such as that ancient symbol of the Eternal City, the Colosseum. To Francesco Rotundi, the project manager for Metro C (the contractor responsible for the new line), the amphitheater presents a technical headache. “The problem is: What happens to the Colosseum when I pass under it with the excavator?” he said, thinking of how the structure’s massive walls could shift as the ground below it settles. “And what happens after I’ve excavated and I pass through with the metro?”

Rotundi’s predecessors would have simply torn through. Rome’s first metro line, built during the 1940’s and 50’s, runs from the central train station to EUR, Benito Mussolini’s ambitious capital outside the capital. Workers dug in open pits as truckloads of history were sifted for valuables and dumped elsewhere. Subsequent expansions have been more cautious, but this new line has been the first to give preservation the same consideration as modernization: more than a year before construction could begin, every access point, ventilation shaft, and escalator tunnel for the planned line had to be examined by teams of archaeologists—a Herculean task by any measure.

“What makes Rome different from other cities is that we can’t plan,” said Luigi Napoli, technical director at Roma Metropolitane, the agency overseeing the subway’s expansion. “We have to go straight to the field and see what challenges await us.”

Ancient Rome didn’t fall so much as scatter and sink. Medieval masons quarried it for its bricks. The Church carted off its marble. Renaissance art lovers collected its frescoes. What preservation did occur happened organically: Walls encased temple columns; an emperor turned a predecessor’s palace into a foundation for his public baths. Century by century, the new grew on the old.

Building a subway line across this palimpsest of history has inspired ambivalence among archaeologists. Some are concerned about what Linea C’s construction might destroy. Others, however, are excited by the rare chance it offers them to excavate in Rome’s historic center. “As urban archaeologists, we can’t decide where to dig,” said Fedora Filippi, who is leading the digs south of Piazza Navona. “We have to gather the opportunities the city gives us.”

Last winter, these opportunities arrived as a patchwork of plywood and tarping—erected to fence off work sites from traffic and tourists—settled over the roads and piazzas of central Rome. Archaeologists took turns in the depths of the dig, while small cranes lowered buckets to pull out 2,000 years of detritus. Caution was justified: the old city had already made itself known. Archaeologists first broke ground in 1999, just outside the Aurelian city walls, seeking a site to slip in the excavator that would dig the tunnels. At their first choice, they found an antique water mill, dating from the 19th century. At their second, they uncovered Roman walls and two children entombed in amphorae.

In the city center, where the digs were hemmed in by trees, traffic, buildings, and the cost of excavation (Linea C doesn’t give breakdowns of its costs, but each kilometer of track in the center is expected to cost $180 million), the finds were generally small: cart-rutted paving stone; shattered frescoes; handfuls of mosaic flooring. When a young archaeologist uncovered a malformed cube of orange-colored ivory—a gambler’s die—her screams of delight had her colleagues scrambling from their pits.

For most archaeologists studying the digs, the greatest discoveries lie in the stretches of dirt between the relics. Each stage in the excavation is a snapshot of ancient topography, and a layer of earth may contain more secrets than the perfectly preserved mosaics below it. Thick clay might mean flooding: a period of abandonment. Scatterings of fingernail-size marble chips suggest an ancient stonecutting workshop.

At a site across the street from the Colosseum, archaeologists uncovered Roman taverns, rough mosaic floors, a few gold ingots, and what looked like a jade pendant. But their attention was focused on a small hole where the paving stones of an ancient road suddenly dropped in a V shape. Nearby, a Roman wall was missing its foundation, hints of medieval builders burrowing underneath the road for imperial marble. “At some point, their tunnel collapsed, dropping the paving stones down with it,” one archaeologist inferred. “Who knows?The next find might be a human skeleton, trapped below.”

In the 19th century, archaeologist Rodolfo Lanciani created the first historical-chronological portrait of Rome when he plotted the ancient city onto the modern in a series of 46 detailed topographic sketches. Some 100 years later, in the office of the superintendent of archaeology, Filippi and her assistants worked on an update. On oversize paper, the kind used by draftsmen, they transcribed finds from scientific texts, archival photos, and longhand notes from more than a century of construction work. Filippi was beginning to cobble together a vision of the Roman city below the Baroque church of Sant’Andrea della Valle, where her digs were centered.

In her southern pit, she had found a thick foundation capped with a block of marble—a colossal brick from a monumental wall. Plugged into her map, the wall ran perpendicular to a long piece of wall discovered in the 1930’s when a road was enlarged. Nearby basements entombed capitals belonging to columns bigger than those of the Pantheon. “Each piece is a piece of the puzzle,” said Filippi. “It indicates we’re in a public area.”

According to historical records, this area once housed two important sites: the Temple of Good Fortune and the Baths of Agrippa, a complex of public pools and gardens dating back to the early reign of Augustus Caesar. But as of yet, they’ve never been unearthed and their exact location remains in the realm of conjecture.

In her site’s second pit, Filippi uncovered stairs dropping to a swath of pavement that crossed an underground canal. At the hole’s far edge lay a wall built with waterproof mortar. Asked what she made of these puzzle pieces, Filippi danced around the subject and hesitated before finally admitting, “I’m speaking very speculatively here. But we might have found something.”

For a moment, the modern city held its breath.

Stephan Faris is a journalist based in Rome.