In 2013, the Italian architect Dario Del Bufalo overheard a one-in-a-million conversation that led to the rediscovery of a priceless, 200-year-old mosaic that once belonged to the Roman Emperor Caligula.

Del Bufalo recently told 60 Minutes that he was signing copies of his book Porphyry, about the red stone popular with Roman Emperors, at the Bulgari store in New York when he heard a young man comment to a woman he was with: “What a beautiful book. Oh, Helen, look, that’s your mosaic!”

He then heard the woman reply, “Yeah, that’s my mosaic.”

Del Bufalo took off after the pair and caught up with the young man, who told him that the mosaic was housed at the woman’s apartment on Fifth Avenue, and was being used to serve tea and coffee.

In fact, Del Bufalo realized, the mosaic was a missing piece of a dance floor made for one of Caligula’s boats. The emperor had commissioned two of the boats, adorned with gardens, silk sails, and even bathrooms, and used them for extravagant floating parties on Lake Nemi. But the third Roman Emperor was so disliked for his brutal leadership that, following his assassination, both ships were sunk.

Mosaic of Caligula. Photo by Ernesto Ruscio/Getty Images

Over the centuries many attempts have been made to recover the boats. In the 1930s, Mussolini dredged the lake and found the remains of the boats, which were put into a museum. But it was in turn burned at the end of the World War II. It is thought that as the chaos of war took hold, the mosaics were stolen before being sold to the woman Del Bufalo overheard at his book signing in the 1960s.

The woman in question was antiquities dealer Helen Fioratti, who said she had bought the mosaic from an Italian family in good faith. While she recognized its beauty, she did not know of its incredible history—or questionable provenance.

“It was an innocent purchase,” Ms. Fioratti told the New York Times in 2017. “It was our favorite thing and we had it for 45 years.”

Del Bufalo notified authorities and prosecutors eventually seized the table based on evidence that it had been stolen. It has since been returned to Italy, where it is now on display at the Museum of the Roman Ships in Nemi, 19 miles outside of Rome.

In his interview with 60 Minutes, Del Bufalo said that he would make a replacement table for Fioratti, adding that “she would never know the difference.”

“I felt very sorry for her, but I couldn’t do anything different, knowing that my museum in Nemi is missing the best part that went through the centuries, through the war, through a fire, and then through an Italian art dealer, and finally could go back to the museum,” he said. “That’s the only thing I felt I should have done.”