A 2,300-year-old coin found after flooding along the River Avon near Bath has revealed details of early maritime activity up the Bristol Channel.
The 20mm coin was spotted in receding floodwaters in 2012, but the owner kept the details private until now.
It has been verified by the British Museum and is understood to be a Carthaginian coin, minted around Sardinia in 300-264 BC.
Several similar examples have been recorded but only from the coastline.
On one side of the coin is an image of Tanit - a Punic and Phoenician goddess - and on the reverse is a horse's head.
Its owner wishes to remain anonymous but has allowed it to be included in a history project in Saltford, where the coin was found.
Project organiser Phil Harding said: "[The coin] predates the Great Wall of China, it predates the Roman Empire, it predates the birth of Jesus Christ, it predates Alfred the Great - it's just fantastic."
Dr Sam Moorhead, who recorded it for the British Museum, said it could have been struck at one of several mints in the Punic Empire, including Carthage and cities in Sardinia.
"It is certainly one of the earliest coins found in Britain," he said, adding other examples had been found from Cornwall, around the south coast to Kent, and up the east coast to Lincolnshire.
"It has been argued for a long time that these coins reflect trade with the Mediterranean, probably often via Gaul.
"The main commodity that Britain had which was wanted by the Carthaginians and others was tin, found in Cornwall and Devon.
"The Saltford coin does suggest that there was maritime activity up the Bristol Channel as well and we can imagine traders entering the River Severn."