In the 1960s, New York City art dealer Helen Fioratti bought a lovely mosaic in Italy from a noble family. She turned the mosaic into a coffee table and used it for decades. Fifty years later, Fioratti was informed that the mosaic was actually a piece of floor from one of Roman emperor Caligula's party ships that sunk after he was assassinated in 41 AD. Now, the priceless artifact is on display at the Museo delle Navi Romane in Nemi, Italy. From The Guardian:
In New York in 2013, [Italian stone and marble expert Dario] Del Bufalo gave a lecture and signed copies of his book, Porphyry, about the reddish-purple rock much used by Roman emperors.
The book included a picture of the long-lost mosaic[…]
The mosaic and other antiquities were recovered from the lake in the 1930s and housed in a lakeside museum. In 1944, as the Nazis retreated from Italy, the ships and many other treasures were burned[…]
as he signed copies of his book, Del Bufalo overheard a man and a woman say the woman had the mosaic they were looking at on the page.
"There was a lady with a young guy with a strange hat that came to the table," Del Bufalo told CBS. "And he told her, 'What a beautiful book. Oh, Helen, look, that's your mosaic.' And she said, 'Yeah, that's my mosaic.'"[…]
The office of the Manhattan district attorney says evidence suggests the mosaic was stolen, possibly during the second world war [long before Fioratti purchased it].