The archaeologist stares down into the enormous hole that edges up to the back of Rome's rugby stadium and gestures helplessly. "Make no mistake, this Roman necropolis we have found stretches right under the pitch."

Marina Piranomonte is talking about the Stadio Flaminio, after seeing how the "City of the Dead" she has dug up behind Gate 7 has fared under the winter rains. With 23 funeral inscriptions, dozens of bronze coins, oil lamps and more than 1,000 ceramic fragments found since digging started in 2008, Piranomonte believes the necropolis could be "immense," containing up to 50 tombs linked by a grid of streets.

"The Via Flaminia [an ancient Roman road] is 120 metres that way," she says, waving at a line of parked cars and modern housing. "It's possible the necropolis extends that far." Turning, she points across the stadium car park. "About 800 metres that way some tombs, spotted during a dig in the 19th century, could form part of the complex."

Despite the risk of jokes about Italy's players getting buried here, the find could prove an extra draw for Six Nations games. In coming seasons, when the dig is finished, visitors will be able to see live rugby and dead Romans on one ticket. Sadly for Wales fans whose team played Italy here on Saturday, they missed out on a glimpse of the five tombs Piranomonte has unearthed to date, since a protective layer of soil placed on top of the remains at the end of last summer will only be removed when digging resumes after the game.

"So far we have found inscriptions with Greek names, which suggest that Greek freedmen [former slaves] were buried here," Piranomonte says. Thanks to the regular flooding from the nearby Tiber, the remains have been well preserved under clay. "The site dates back to the first century BC, but medieval pottery suggests the tombs became dwellings after the Romans. We have found staircases installed by people who built second floors over the tombs for extra rooms."

The find puts the stadium on a par with other Rome buildings that boast their own private Roman digs. Even the Ikea carpark on the ring road has a chunk of Roman masonry on display.

Rugby fans unsatisfied with imagining what lies behind the cordoned-off dig at the stadium this season can head for a coffee to the nearby concert-hall complex, which was shunted a few yards during construction when builders discovered and restored a Roman villa.

That lucky find apart, archaeologists know a wealth of tombs and villas that followed the Via Flaminia out of town now sit hidden beneath scruffy factories and mechanics' workshops. Eyeing the Roman tomb that disappears under the back of the stadium, Piranomonte says she suspects that Pier Luigi Nervi, the ground's architect, had not let Roman heritage get in his way when he dug his foundations in the late 1950s. "I think he saw the tombs but pushed on without telling anyone."

Nervi's flowing, curvaceous stadium is itself an architectural jewel in a neighbourhood that has become a Roman enclave for modern building. The must‑see Maxxi modern art gallery, designed by the London-based Iraqi architect Zaha Hadid, is five minutes away and is hosting an exhibition dedicated to Nervi's work.

Next to the gallery is a disused weapons factory that mayor Gianni Alemanno wants to level and rebuild as an opera house. Alemanno is also mulling moving rugby matches to the nearby Stadio Olimpico from the smaller Flaminio.

Back at the stadium, Piranomonte is preparing for this summer's dig and has only another 20 metres of asphalt she can excavate before she gets to the street. "I feel it is very apt to dig here since rugby has it roots in the Roman game of harpastum," she says. Exported around the empire by legionaries, harpastum involved keeping possession of a ball by skipping tackles and passing to team‑mates. The exact rules are unknown, but it is clearly similar to rugby.

"The game took off in Britain and we have a source who recounts how the Romans were defeated 1-0 by a British team in 276AD," she says. "This was the first in a series of defeats that has not yet stopped unfortunately, but at least I am hoping the British will be envious of our necropolis."