The cold glint of hard currency dug up by metal-detector enthusiasts is revealing the forgotten lives of English traders and citizens during the Dark Ages.
Numismatists at the Fitzwilliam Museum in Cambridge, with the help of amateur treasure hunters, have created an online index of 6,500 Anglo-Saxon and Norman coins.
The medieval coin corpus is giving scholars the opportunity to analyse statistically significant quantities of data from formative episodes in English history.
It has already revealed evidence of a glut of silver currency swamping Anglo-Saxon kingdoms during the 8th century.
This appears to have been followed by a great scarcity of silver coins, which some archaeologists may have misinterpreted as marking the collapse of commerce at particular sites shortly before the Vikings arrived.
The possible sites of seasonal markets have emerged from the data where large numbers of individual coins have been retrieved but no buildings detected.
These include one at Brandon, Suffolk; a second near Royston, Hertfordshire; and a third near Tilbury, Essex.
As the coins from the potential market sites mainly date before the mid-9th century, it suggests trade may have retreated within fortified towns to escape Viking raiders.
Mark Blackburn, keeper of coins and medals at the Fitzwilliam Museum, said the database enabled academics to pursue sophisticated lines of inquiry.
Numismatists have previously relied on Dark-Age coin hoards, often buried in times of war. Individual finds give a far better indication of how coinage was actually used.
While some of the data was gleaned from museum collections, the corpus is dominated by the findings of metal-detector enthusiasts who have discovered unprecedented quantities of Anglo-Saxon and Norman coins since the 1980s.
They have been encouraged to bring in the currency so that it can be catalogued, weighed and photographed.