A 2,000-year-old artifact that had ended up in the home of a Manhattan antiquities dealer is now in an Italian museum. NEMI, Italy — If stones could speak, the mosaic unveiled recently at an archaeological museum just south of Rome would have quite the tale to tell. It was crafted in the first century for the deck of one of two spectacularly decorated ships on Lake Nemi that the Emperor Caligula commissioned as floating palaces. Recovered from underwater wreckage in 1895, the mosaic was later lost for decades, only to re-emerge several years ago as a coffee table in the living room of a Manhattan antiques dealer.