Retired police officer Tom Thomas, from Reading who has been a detectorist for over 30 years found the coin in the 90’s but didn’t realise it was one of a kind until a fellow detectorist pointed it out at a family barbecue.
He found the coin, which dates back to 286-93AD, in a farmer’s field in Berkshire.
“I didn’t know what it was as such. I put it with my small collection and thought nothing more of it,” he said.
It turned out to be the only known example of a Carausius Denarius coin which features the Roman goddess Salus feeding a snake rising from an altar.
Friend Mark Becher, who runs a detectorists’ group in Aylesbury, Buckinghamshire, had been at a barbecue at Mr Thomas’s house.
“I was staggered when I saw the coin,” he said.
“I’ve been metal detecting for more than 25 years and I’ve witnessed countless finds, both my own and other people’s. I’d just never seen anything like it.”
Mr Thomas is now selling the coin at auction.
He said: “The only reason I’m selling it now is because it’s so unique and valuable it has to be locked away in a bank vault.”
The rare coin will be auctioned at Hansons Auctioneers on 27 August, and has a guide price of £10,000.
Photos courtesy of Hansons Auctions