The excavator bucket had barely broken through the top layer of fill when it scraped something that was not rubble.
Beneath Piazza Pia in Rome, in the shadow of Castel Sant’Angelo, a crew building a traffic underpass had hit a stone washing tank.
Then more tanks. Then a mosaic floor.
What sat under their feet was a Roman laundry, complete enough that the tubs still held their shape after nearly two millennia underground.
A find like this has frozen Roman building sites before. Would this one stop the job?
Why the laundry moved instead of the underpass
Rome has been continuously built on for more than 2,000 years, and every shaft sunk into it is a lottery. Italian heritage rules require crews to stop when significant remains appear so archaeologists can assess them, which is why tunnel work in the capital so often stalls. On the Metro C line, decades of finds slowed construction until a planned station in the dense historic center was dropped from the design altogether.
At Piazza Pia the answer was emergency archaeology. Because the remains sat squarely in the footprint of the new access ramp, the heritage authorities approved a plan to record the structures, take them apart and move them, rather than redesign the tunnel around them. Relocation means the artifact travels; the alignment does not.
The underpass itself exists to take vehicle traffic away from the square entirely, freeing the route between Castel Sant’Angelo and St. Peter’s for pedestrians ahead of the Jubilee. The mayor’s office framed the outcome as a double win, saying the finds would be protected while, as Roberto Gualtieri put it, the project would still finish on schedule.
What a Roman laundry looks like when the fill comes off
A fullonica was an open air facility for washing, treating and preparing cloth and clothing. Several stone washing tanks used for pressing survived, along with large buried vessels called dolia used for soaking cloth in detergent. That detergent was usually fermented urine, whose ammonia content made it an effective degreasing agent for wool.
The Tiber runs barely a block away, and that proximity guaranteed the rapid, abundant water supply any fullonica depended on. Alongside the tanks, the dig produced a mosaic floor and quantities of ceramic fragments.
Below the workshop lay something older still: the foundations of a travertine wall and a colonnaded portico bordering a large garden that once overlooked the right bank of the river.
What the dig found stacked under the tubs
The roman fullonica underpass excavation dated the laundry to the high imperial period, the second to third century AD, built on top of an earlier suburban imperial residence. Work directed by the Special Superintendence of Rome identified three building phases in the garden layer, spanning the years between Augustus and Nero.
The dig also recovered a notable series of Campana slabs, figured terracottas carrying unusual mythological scenes. They had not stayed on a roof. Later builders reused them as covers over the drains serving the laundry, which is exactly how they survived intact.
Near the garden level, archaeologists lifted a lead water pipe stamped with the name of the water supply’s owner. The inscription reads C(ai) Caesaris Aug(usti) Germanici, pointing to the emperor Caligula and placing the site inside the Horti Agrippinae, the riverside gardens associated with his mother, Agrippina the Elder.
What the name on a lead pipe told the crew
Archaeologists have noted that a monumental portico separating those gardens from the Tiber matches a scene described by Philo of Alexandria, though that identification rests on interpretation rather than on the pipe alone. Still, a stamped imperial name is a rare find at any depth.
The construction job around that find was its own feat. Work began in August 2023 and ran 450 days, with about 110 people on site around the clock across three shifts. The operator used a cut and cover, top down method so crews could work at street level and inside the box at the same time, a sequencing logic familiar from other large urban tunnel builds where schedule pressure is relentless.
The trickiest piece was not archaeology at all. A sewer bypass was dug between diaphragm walls next to the existing main collector, and only once that bypass was running could the original collector be demolished. The new stretch extends the existing Lungotevere in Sassia underpass by about 425 feet, and more than 45,000 cubic yards of earth came out.
What the engineers left behind and what the piazza became
On 23 December 2024, the day before the Holy Door opened, the square was handed back to the city. Surface traffic was gone, replaced by a pedestrian space with two large fountains, new lighting and replanted greenery. The total investment was €85.3 million, roughly $89 million at the time, and the mayor’s office confirmed the project as completed within timescale.
The fullonica itself is being restored and reassembled in the gardens of Castel Sant’Angelo, only a short distance from where it was found, with smaller finds displayed inside the castle. That decision mirrors the approach at historic sites elsewhere where keeping artifacts near their original ground matters as much as the conservation work itself.
What is not settled is whether the same approach scales. Rome’s deeper metro works are still pushing toward the historic core, and each one meets the same layered ground under the same clock.
