The origin of one of the British Museum's greatest Roman treasures has been thrown into confusion after a scholar claimed it was actually made in the 16th Century.
The Portland Vase was thought to have been found in 1582
Dr Jerome Eisenberg, one of the world's leading authorities on ancient art, is "convinced" that the Portland Vase was made during the Renaissance.
The vase is described by the museum as "the most famous cameo-glass vessel from antiquity" and was a widely accepted to have been made circa 30-20 BC.
A museum expert said the vase was still believed to be Roman because of the techniques used to make it.
Dr Eisenberg, editor-in chief of ancient art and archaeology magazine Minerva, has been on a personal quest to establish the origin of the vase for 32 years.
In the current issue of Minerva, he wrote that it was thought to have been found in the tomb of Emperor Severus Alexander in 1582.
But "numerous stylistic inconsistencies" - meaning some images were closer to Renaissance style than Roman - meant it was likely to have been made in the second half of the 16th Century, he wrote.
The scenes on the vase had been interpreted in more than 50 different ways, he wrote.
Confusion over the vase's figures arose because they were created "by a brilliant later 16th century artist, perhaps an engraver of cameos".
'Not a forgery'
The artist, who did not have a true knowledge of classical mythology, probably based his work on an early 3rd Century marble relief, he argued.
"The sea-monster depicted in the lap of the reclining female figure on the Vase provides the principal clue to my redating of this cameo glass masterwork," Dr Eisenberg wrote.
He added that he did not consider it to be a forgery - but still "one of the world's greatest art treasures".
The British Museum's deputy keeper of Greek and Roman antiquities, Susan Walker, said the vase was created using the Roman technique of "dip-overlay" - which was not understood until recently.
"Disagreement over the interpretation of the iconography is no reason to suppose that the object in question is not ancient," she said.
"However... there is good reason to advance the date of the Portland Vase by a few decades, from the late first century BC into the early first century AD."