From the Telegraph:

Experts are excited about a rare coin unearthed by an amateur treasure hunter which could change the accepted ancient history of Britain.

The silver denarius which dates back to the Roman Republic — before Julius Caesar made Rome an empire — was unearthed near Fowey in Cornwall.

Dating from 146 BC, it shows how ancient Britons were trading with the Romans well before the country was conquered in AD 43.

"It proves that there was a lot more going on between the continent and ourselves," said Anna Tyacke, Finds Liaison Officer at the Royal Cornwall Museum.

Cornwall had trade significance because of the tin and copper it produced, but that economic activity is not well documented before the third century AD.

Coins were relatively rare, of high value and often stayed in circulation for more than 100 years — which makes dating the find harder.

Sam Moorhead, Finds Adviser of Iron Age and Roman coins at the British Museum, said: "It may have been the wages of a Roman legionnaire, who earned about 300 denarii a year in the Roman imperial period — after the conquest.

"You could probably have got about eight loaves of bread for a coin like this, or eight litres of wine.

"Vineyard labourers would have earned between a half and one denarius a day. Whereas to be a senator you had to have at least 250,000 denarii in the bank."

The silver coin was minted in Rome and carries the likeness of Roma wearing a winged helmet, plus the name of a Caius Antestius, its maker.

"Roma is a personification of Rome, rather like Britannia is a personification of Britain," Mr Moorhead explained.

The reverse of the coin carries a picture on horseback of the mythological twins Castor and Pollux, who were believed to have helped the Romans in battle.

I think we're reading an awful lot into this one ... until you find rather more examples, it's a leap to connect it to trade between Romans and Britons ... one also can't be sure if it came directly from a Roman or through continental intermediaries ...