Lasers provide clues to an early medieval money mystery

Human-made currency such as coins and paper bills have certainly evolved over time. Small pieces of precious metals or paper with no metal backing have changed into invisible cryptocurrencies stored on servers. For decades, numismatists–or currency experts–have puzzled over where the silver present inside some coins uncovered in England came from. The coins date back to between 660 and 750 CE, when the Anglo-Saxon world began to see a large revival of trade using silver coins. This shift broke the reliance on gold and archaeologists have uncovered about 7,000 of these silver pieces.

Now, a new noninvasive way of peering into the past may have revealed where the silver from the coins came from. It offers clues into how political changes and the rule of Charlemagne–the Holy Roman Emperor and King of the Franks–fueled currency changes in early medieval Europe. The findings are described in a new study published April 8in the journal Antiquity and could deepen modern understanding of the continent’s economic and political development at the time.

[Related: Benjamin Franklin used science to protect his money from counterfeiters.]

“There has been speculation that the silver came from Melle in France, or from an unknown mine, or that it could have been melted down church silver,” study co-author and University of Cambridge early medieval English historian Rory Naismith said in a statement. “But there wasn’t any hard evidence to tell us one way or the other, so we set out to find it.”

A little help from lasers

Earlier research tested other coins from a silver mine at Melle, but this new study looked at less-studied Fitzwilliam’s coins. These 49 silver pieces were minted in England, the Netherlands, Belgium, and northern France and date from 660 to 820 CE. They are housed by The Fitzwilliam Museum in Cambridge.

Jason Day from Cambridge’s Department of Earth Sciences traced what elements were present in the coins in a lab. Day then used a technique called portable laser ablation. During this process, microscopic samples were collected onto Teflon filters to analyze the lead isotopes presented. This new technique pioneered by the Vrije Universiteit in Amsterdam, combines a minimally invasive sampling with a laser and the high precision results of the more traditional methods that take samples of metals.

While the coins primarily continued silver, the amount of gold, another metal called bismuth, and other elements guided the researchers towards the silver’s previously unknown origins. The various ratios of lead isotopes in the silver coins also provided further clues to where the metals originated from.

Byzantine silver for the masses

Twenty-nine of the coins in the study date back to 660 to 750 CE. They were minted in present-day England, France, and a cross-border cultural region in Northwestern Europe called Frisia. However, the lasers revealed very clear chemical and isotopic signatures that matched 3rd to early 7th century silver that came from the Byzantine Empire in the eastern Mediterranean.

This Byzantine silver was homogenous across the coins. No known source of European ore matches the elemental and isotopic characteristics of these early silver coins. According to the team, there is also no meaningful overlap with late Western Roman silver coins or other objects made from the metal, meaning that it was not simply recycled late Roman silver.

“These coins are among the first signs of a resurgence in the northern European economy since the end of the Roman Empire,” study co-author and University of Oxford archaeologist Jane Kershaw said in a statement. “They show deep international trade connections between what is now France, the Netherlands and England.”

The study proposes that the Byzantine silver must have made its way into Western Europe decades before it was melted down, as the late 7th century is considered part of the Dark Ages, or more accurately termed Migration Period. This was a low point in trade and diplomatic contacts as the Roman Empire ended.

[Related: Divers recovered a treasure trove of more than 30,000 ancient, bronze coins off the Italian coast.]

“These beautiful prestige objects would only have been melted down when a king or lord urgently needed lots of cash. Something big would have been happening, a big social change,” said Kershaw. “Elites were liquidating resources and pouring more and more money into circulation. It would have had a big impact on people’s lives. There would have been more thinking about money and more activity with money involving a far larger portion of society than before.”

The team hopes to look further into how and why so much silver moved from the Byzantine Empire into Western Europe. It was potentially a mixture of trade and payments to Anglo-Saxon mercenaries serving in the Byzantine army.

The rise of Frankish silver

The study also pinpointed a shift away from Byzantine silver to a new source of metal. They analyzed 20 coins from 750 to 820 CE and found that the silver was quite different by this time. It had lower levels of gold, which is characteristic of the silver that is mined at Melle in western France. Mining here was particularly intense during the 8th and 9th centuries.

The team believes that Melle silver permeated regional silver stocks after 750 CE and was mixed with older, higher-gold stocks, including Byzantine silver. While it was already known that Melle was an important mine at this time, what was not clear was just how quickly the site became a major silver producer.

The study argues that this widespread suge in Melle silver was driven by Charlemagne. He is best known for uniting Western Europe by force and he took more control over how and where the coins of his kingdoms were made. The management of silver supply likely went alongside the other changes introduced by Charlemagne, his son, and grandson. These monetary changes include altering the size and thickness of coins and marking their name or image on the coins.

“I strongly suspect that Charlemagne did something similar with Melle silver,” Naismith said. “We can now say more about the circumstances under which those coins were made and how the silver was being distributed within Charlemagne’s Empire and beyond.”