It has long been rumored that a shipwreck in the distant past sent a precious Roman marble statue – a rare copy of a fifth-century BC depiction of the “Doryphoros”, or spear-bearer – into the depths of the seas off Italy. That was the story given in the late 1970s when the statue appeared out of nowhere in Munich’s Glyptothek, the city’s museum of ancient Roman and Greek art.

A dealer had loaned it to the museum in anticipation of a possible sale, and the story he then told was of an image saved from the ravages of seawater and kept in a private collection, where it escaped notice for decades. And that was the account approved by officials at the Minneapolis Institute of Art when they bought the statue in 1986 for $2.5 million and installed it as a signature artifact in a showcase gallery.