The Metallurgy of Roman Silver Coinage
This is a long term project based at the Universities of Liverpool and Warwick that is investigating the chemical composition and metallurgical structure of Roman silver coinage from the reign of Rome’s first emperor, Augustus (27 BC - AD 14), to the fourth century AD.
The Romans produced coins in a variety of metals: gold, silver, brass, bronze and copper. The fineness of the silver coinage has often been used to gauge the state of the Roman monetary economy. Initially the main unit of silver coinage, the denarius, was produced from pure silver bullion, but from quite early on the emperors began adding copper to debase the alloy. The long term trend was towards increasing debasement over time. By the second half of the third century this coinage contained only about five percent silver or even less. It is thought that these debasements were the consequence of the depletion of silver stocks within the empire coupled with an ever-increasing state budget to finance wars and armies.
However, although the long term trend was one of incremental debasements, our work has shown that there were a number of attempts to reverse this trend by increasing the fineness of the denarius. This suggests a more complex approach to the production of silver coinage on the part of the Roman state than was previously thought.
The denarius coinage was produced mainly at the mint of Rome, although they were sometimes made at other locations in the empire as well. The resources and refining technologies employed at these provincial mints differed from those of Rome, and detailed analysis of impurities in the silver coinages can help to characterise the products of different mints, sometimes allowing us to pinpoint the likely place of production in those cases where the place of minting is uncertain. Such analyses also allow us to highlight changes in resources at the mint of Rome.
Aside from the denarius coinage, mints in the Roman provinces also produced silver coins of a local type. These too have been investigated in order to compare their silver contents with the denarius coinage and with each other. As with the denarii, an analysis of the impurities present in these issues can help to characterise the products of different mints, and also shows how some of these coinages were in fact produced centrally at major mints like Rome, Antioch and Alexandria.
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