A metal cup acquired by a rag and bone man from Somerset has been revealed to be a pure gold goblet from the 3rd or 4th Century BC, worth up to £500,000.
The vessel has two female faces looking in opposite directions with their foreheads decorated with a snake motif.
William Sparks, who ran a scrap metal business in Taunton during the 1930s and 40s, left the ancient treasure to his young grandson John Webber.
The goblet is to be sold by Duke's
auction house in Dorchester, Dorset.
Mr Webber, 70, said: "My grandfather was originally a proper rag and bone man from Romany stock and lived in a caravan.
The goblet has been crafted from a single piece of gold
"My father died in the war and afterwards my grandfather gave me some things shortly before he died.
"One of the things was the cup which I remember playing with. Because he mainly dealt in brass and bronze, I thought that was what it was made from."
After forgetting about the cup for years he rediscovered it last year when he moved house.
"I sent it to the British Museum and the experts there hadn't seen anything like it before and recommended I had it tested at a laboratory," said Mr Webber.
The analysis confirmed its age and that it had been painstakingly crafted from one piece of gold.
Peter Northover, the scientist who reported on the gold analysis, said in the report: "The method of manufacture and the composition of the gold are consistent with Achaemenid gold and gold smithing."
The Achaemenid empire was based around Persia, but at its height stretched from Iran to Libya. It was wiped out by Alexander the Great in 330 BC.
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