Every year the snow formed a new layer in the ice. When scientists went through the layers more than 2,000 years later, they saw a clear decrease in lead pollution in the ice from the years around the late Republic. And yet we know that coin production continued during this period.
Jonathan Wood and Matthew Ponting are experts in the field of archaeological metallurgy. Their new research, funded by the University of Liverpool, suggests the reduction in pollution is down to recycling.
Crisis led to shortage of new silver
The Roman Empire had rule between 139 and 33 B.C. big problems. This period, also called the ‘crisis of the Roman Republic’, was characterized by civil wars and uprisings. These were so violent that they eventually led to the end of the republic – after which Julius Caesar became dictator and later Emperor Augustus came to power, who turned the empire into a monarchy.
The crisis left Rome without access to silver mines on the Iberian Peninsula and in southern France. As a result, the Roman Empire had to reduce the purity of the silver in coins such as the denarius, for example by mixing copper into it.
The reduced purity of silver coins is known from previously analyzed coins – but the lower silver content does not fully explain the decrease in lead pollution in Greenland’s ice.
Wood and Ponting therefore analyzed another metal in the silver coins: gold. All silver produced in ancient times contained small amounts of gold, which was mined at the same time as the silver. The gold content hardly changes when silver is refined. As a result, gold content can be used to determine whether silver coins are made from silver mined in the same area.
In general, Roman silver has a fairly high gold content, but around 120 BC. – so during the crisis years – many silver coins with a much lower gold content were suddenly produced. Later that century, the coin metal was mixed with other silver, which in turn resulted in slightly higher gold contents.
The researchers conclude that the Romans started minting new coins from silver that they had not mined themselves. This silver was possibly plundered after conflicts in Iberia, southern France and Asia Minor (modern Turkey).
It seems that in 49 B.C. a new supply of silver with a higher gold content came into circulation – the same year that Julius Caesar returned to Rome after his victory over the Gauls. The researchers therefore suspect that the new silver was stolen from the Gauls by Caesar’s army.
Recycling was good for the Roman economy
The research suggests that the amount of silver in some coins has been reduced to allow more coins to be minted from the same amount of silver, but previous research indicates that this method of devaluing coins should still lead to measurable lead pollution in Greenland’s ice. The sharp decline must therefore mean that silver mining itself declined drastically as the Romans began melting plundered silver from other countries into their own coins.
The Romans were far from the first to do this. On stone tablets from the 19th century BC. found in the ruins of Mari in modern-day Iraq, for example, report a similar practice. But this is some of the earliest tangible evidence that it happened on a large scale.
Wood concludes: ‘Devaluing silver was a way to deal with fluctuations in the silver supply. Another way was to melt down existing silver, yours or someone else’s. For the Romans, recycling coins would have been significantly cheaper than mining new silver – beneficial for their economy and the environment.’