An "incredible" gem has been re-dated to an earlier period and may have been owned by a high-ranking Iron Age chieftain, experts have said.
The gem, mounted in an iron ring, depicts the armed god of Mars and was found in Colchester, Essex, in 1995.
Experts have re-dated it to 200 BC, some 150 to 250 years earlier than previously thought.
Curator Glynn Davis said the new date meant it could have been owned by an "influential Iron Age Briton".
The deep red engraved gem, an intaglio, would have been used by its owner to seal letters and documents and was excavated on the site of a Romano-Celtic temple.
Its revised date came about during research for the recently launched online collections database at Colchester and Ipswich's Museums Service.
Rev Dr Martin Henig, an expert on ancient engraved gems, said its shape and style dated to the 2nd Century BC and no later than the 1st Century BC, long before the Roman Emperor Claudius's invasion of Britain in AD 43.
Writing in his museum blog, Mr Davis said it was "very likely to have arrived in Britain on the finger of a solider, as part of the invasion of Britain, a family heirloom passed down generations of the family".
But he added that, more speculatively, it could have been owned by an Iron Age Briton, "traded from the Romans decades before their invasion".
"In this instance, it may not be Mars that the owner saw upon this ring, but Mars Camulos - the ancient Britons' own god of war," he added.
The intaglio can be viewed online and in person when Colchester Castle can re-open following government guidance.