Archaeologists excavating Notre Dame Cathedral in Paris have uncovered centuries of buried history, including a 1,700-year-old Roman coin and baffling markings that experts still can’t explain.

The excavation, which has been in the works for years, began after the cathedral was rebuilt in the wake of a devastating 2019 fire. The latest results were reported earlier in June by the Associated Press (AP). 

Digging in the cathedral’s forecourt, archaeologists have searched roughly 13 feet below ground for remnants of the city’s past.

Among the finds are a 4th-century coin bearing the face of Emperor Constantine, as well as medieval pottery fragments bearing markings archaeologists have not yet deciphered.

One image shows a medieval pottery fragment recovered during the excavation, one of several ceramics unearthed beneath Notre Dame.

Archaeologist Valentine Breloux told the AP it’s “rare to find complete ceramics,” adding that the most astonishing discoveries were mysterious reddish markings painted inside pottery fragments — which experts have yet to decipher.

The excavation, which French media has called the “dig of the century,” has also yielded hundreds of other objects, including whole jugs and cups that were thrown into a latrine.

The latrine, which doubled as a garbage pit, also contained broken plates and animal bones.

Archaeologists also uncovered medieval grain pits, which were used to preserve harvested grain, from the sixth to the 10th centuries.

A Roman-era doorstep was also discovered at the site, which archaeologists said had been removed from a larger structure, flipped upside down, and repurposed as road paving.

Lucie Altenburg, a conservator with the Paris archaeology unit, told the AP the excavation is a “rare opportunity.”

“The hope is that we are able to go back in time even further than we’ve ever been before,” she said.

The project gives archaeologists a chance to “work on something that’s tangibly going to make a difference to the history of Paris,” added Altenburg.

The Roman finds are among the artifacts archaeologists value most, the AP reported, though the team hopes to uncover evidence of the Gauls, who predated the Romans in the area.

“Here you can see the layers — medieval Paris, Roman Paris, maybe even before that,” archaeology student Yasmine Benali told the AP.

Benali added, “It makes the city feel less like a postcard and more like something still being discovered.”

The dig is tied to a broader renovation of the Notre Dame square, which is expected to add trees and other visitor-friendly features by 2028, according to Altenburg.

Emily Carter, a tourist from Manchester, told the AP that the excavation “makes Notre Dame feel alive again.”

“You come to see the cathedral, then realize there’s another city under your feet,” she said. 

“That’s almost more moving.”

The Associated Press contributed reporting.