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Silver Isotopes and the Rise of Money

Periodic Reporting for period 2 - SILVER (Silver Isotopes and the Rise of Money)

Reporting period: 2019-04-01 to 2020-09-30

Smelting, the extraction of pure silver from its ores in the presence of lead, allowed humans to benefit from silver since the Bronze Age, yet, for more than two millennia, it remained a luxury commodity in much the same way as amber, ivory, and myrrh. Hoards from Mesopotamia and the Levant show that silver was traded in bulk but it would take a long time until the advent of money. The first electrum coinage struck by the Lydian kings in the 7th century BCE did not survive the scarcity of gold and never achieved the status of money in the sense we know it today. The rise of silver coinage in the 6th century BCE in Western Asia Minor and Greece, attested to by the contamination of peat bogs and ice by the atmospheric Pb fumes of smelting all the way to the Arctic, remains an active subject of debate. Some scholars emphasize that the advent of coinage kept pace with the mercenary service, whereas observing that lead contamination trails the number of shipwrecks in the Mediterranean, suggested that the purpose of coinage was to nourish trade and tribute. In the meantime, many powers, including Persia, Sparta, Carthage, and Rome, remained wary of silver monetization for centuries.
Although the ancient link between money and precious metals has been progressively dissolved, the rise of silver money still resonates with modern economy. ‘What is money?’, a commodity or rather a standard of value, is still a modern question. This question is probably better formulated in societies in which credit was not as common as today, central banks did not exist, and different forms of metal coexisted, notably coinage, silverware, and cult objects.
The objectives of the SILVER project relate to these questions by using lead and silver isotopes as a tracer of metal extraction, minting, and circulation. Lead is a metal always found in trace amounts in silver objects and the relative proportions of its isotopes vary over a broad range in rocks as a result of uranium and thorium radioactivity and local geology. Lead isotopes have been used for half a century by numismatists to fingerprint the ore deposits serving as the source of silver. A major ambiguity is that lead used for smelting may simply be foreign to the silver ore. Silver isotopes, which have been introduced to numismatics by our group in 2011, are not affected by this ambiguity because they belong to the metal that carries the value. Their relative abundances, however, unfortunately vary over only a very narrow range since, contrary to Pb isotopes, the cause of variation is purely thermodynamic. Measuring silver isotope compositions therefore require more work to achieve the needed precision for them to be useful. The purpose of the proposal is twofold. First, the development of early coinage in Greece, Ionia, and the Eastern Mediterranean will be traced. The relative weight of each production locality and the proportion of minted metal will be assessed. Second, we aim at monitoring the advance of monetization of the Mediterranean through the rise and fall of the competing empires, notably Persia, Greece, Macedon, Carthage, and Rome. We hope that collaboration between geochemists with a strong analytical and geological background and expertise and experts of history and numismatics will be decisive in documenting the rise of money from a new perspective.
The first part of the SILVER project has accomplished a number of critical tasks. In parallel with the construction of the analytical facilities and the hiring procedures (technical staff and post-doctoral fellows), the isotope fractionation factors between the different silver species present in hydrothermal solutions have been evaluated by cutting-edge methods of nuclear chemistry. Chromatographic methods required to separate and purify silver from coins, artefacts, and ores have been developed or improved as well as integrated with Pb purification chemistry on the same objects. A major hurdle has been and continues to be the sampling of silver coins. The curators of all the major collections we have approached for samples decline drilling. The alternative techniques we then developed as a consequence of this standpoint, which consist in etching the edges of coins, also have not met with curators’ consent. A very successful workshop run by SILVER at the Louvre Museum in Paris in early February 2020 was attended by curators, geochemists, historians, and numismatists and produced new guidelines for scientific sampling.
A survey of lead isotopes in denarii minted by the Roman Republic demonstrated a major gap between the coins struck during the 2nd Punic War and those produced during the second half of the 2nd century BCE and after, which demonstrates a major shift in silver supply. The next step was the study of correlated variations of silver and lead isotopes in Roman denarii, which showed that the coins of the 2nd Punic War were struck from recycled silver in bulk and pre-existing coinage corresponding to the war indemnities paid by Carthage at the end of the 1st Punic War. In contrast, the Roman silver coinage of the late 2nd century was struck from silver produced in Spain using smelting processes developed by Phoenician colonists since the 8th century BCE.
The Roman denarii contrast with the coinage of classic Greece and its colonies in their visible decoupling of silver and lead ores. The Greeks and most of their colonies seem to have been using local lead to extract silver, whereas Phoenicians, and after them Carthaginians and Romans, had to bring foreign lead to the sites of silver extraction. This suggests that the silver ores used by the Greeks were essentially lead carbonates and sulfides, whereas in the Iberian Peninsula silver-rich sulfates had to be combined with lead extracted from galena.
The gap of well over 60 years between the conquest of Iberia silver ore deposits during the 2nd Punic War and the onset of massive minting of silver coinage testifies to the misgivings of Rome with respect to money until the 2nd C. BCE. As attested to by the predominance of unminted silver displayed in the Roman triumphs of the 2nd century BCE, these qualms were shared by many Mediterranean cultures. Why the Roman Republic finally gave in to monetization, probably upon pressure of the bulging mass of copper asses, and engaged into mass production of silver denarii, is unclear. Regardless of the motivations, this period marks the generalization of money around the Mediterranean.
The future results we hope to obtain during the second half of the SILVER project should shed some light on the dynamics of monetary silver mass in the Eastern Mediterranean in the 6th-4th centuries BCE. From our unpublished, still incomplete data sets, it is already clear that Athens acted as a monetary hub for the whole region. The coupling between silver and lead isotopes in ores and coinage should illuminate the smelting process, the relative importance of the different mining districts, in particular Thrace vs Attica, and their evolution through time. One particularly important question is the origin of Persian silver (sigloi and silverware): how much was derived from the huge tributes paid by the Aegean world, and how much was derived from mines of Persia and eastern-most territories? Silver and lead isotopic work on silver money struck by Alexander and the Hellenic world should be critical in answering these questions.