Tracing the origins of early medieval silver coinage

During the mid-7th century AD there was an abrupt economic shift in north-west Europe, particularly around the North Sea, with silver coinage largely replacing the use of gold. Recent research has suggested that at least some of this coinage was produced from a large silver mine located at Melle, in present-day France, with evidence from glacial ice in the Alps showing a significant spike in lead pollution during this period (see CA 347). Now further research has assessed the isotopic and chemical signature of the coinage itself to identify its sources, revealing that silver from the Byzantine Empire – not Melle – was behind the emergence of pennies in north-west Europe.

To identify the source of the silver, a team from the universities of Oxford, Amsterdam, and Cambridge sampled 49 coins (below) of the period, from the collections of the Fitzwilliam Museum in Cambridge and originally hailing from England, the Netherlands, and eastern Francia. Using laser ablation, the team were able to remove microscopic samples to test their lead (Pb) isotope ratios. They found that the coins sorted into two groups, representing two distinct metal sources dating to either side of c.AD 750.

For the early coins, no known European ore sources matched the Pb isotopic signature. Instead, the lead from these coins is similar to that found in Eastern Roman/Byzantine silver from the 3rd to early 7th centuries AD. In their paper, recently published in Antiquity (https://doi.org/10.15184/aqy.2024.33), the team argue that ‘Byzantine silver seems to have served as the bullion for early coinages in regions bordering the North Sea for the entirety of the period c.AD 660-750’, and that it appears to have been recycled from existing plate stocks since east–west trade during this period was in decline. The Byzantine silver tableware buried in Sutton Hoo, Mound 1, is representative of this stock: if melted down, the treasure could have produced 10,000 pennies. It thus appears that the shift to silver coinage was not due to a sudden new availability of the precious metal but was instead driven by other factors.

The later coins that the team analysed, starting in the mid-8th century, displayed a distinctly different Pb isotopic signature, reflecting the fact that the stock of Byzantine silver had dried up by the mid-8th century. The silver from these coins appears to have been largely sourced from the mine at Melle, particularly after c.AD 793 when Charlemagne, and to a lesser extent Offa of Mercia, led a period of coin reform. This aligns well with the glacial ice research that suggests exploitation of the Melle mine began in the late 7th century and reached its peak in the 8th and 9th centuries. It shows, further, that England was dependent on silver from Francia: Offa could not have struck coinage without silver from Charlemagne.

The research was funded by an ERC Starting Grant awarded to Jane Kershaw and an AHRC grant awarded to Rory Naismith.

Text: Kathryn Krakowka / Image: The Fitzwilliam Museum, University of Cambridge