A looted mosaic that once decorated a ship of the Roman Emperor Caligula and ended up as a coffee table in New York City finally returned home Thursday, as details emerged about the lucky break in the investigation that got it there.

Officials unveiled the mosaic at the Museum of Roman Ships, which was built in the 1930s specifically to house the treasures of two huge ceremonial ships Caligula commissioned in around AD 40. The ships eventually sank and were excavated from the depths of Lake Nemi, in the Alban hills south of Rome, starting in the late 1890s.