I wrote this post a little while ago. I thought it was high time to publish it.
An article came out on May 8th2018 in the Proceedings of the National Academy of Sciences of the United States of America describing lead concentration found in ice cores of Greenland. The results have been widely discussed in press: the news website cbc.ca, the New York Times, as well as an awful article in the Atlantic. The article aims to show that important events in the Roman Empire can be found in the ice core by measuring levels of lead and copper.
How these measurements correlate to the history of antiquity is tricky to explain. Lead was an integral component of the Roman silver coinage. The authors of the article mention that “crushed lead–silver ores were roasted and smelted at ∼1,200 °C for some 10 h in small, hemispherical clay furnaces.” These levels of pollutions would find their way to Greenland where they would be deposited in the ice cores. So, testing ice cores for lead concentration allows climate scientists to have an idea of the overall production of silver in the Roman world through time. The findings of the study are important: the second century was a period of intense lead pollution, the third and the fourth, not so much. Plagues correlate well with decreased lead pollution as well. It seems, therefore, that lead production correlates well with perceived ideas of the history of the Roman Empire.
Before moving forward, it is worth mentioning that the findings of this team are crucially important for further study. There are, however, important problems that need to be addressed, not least of all that the correlation between the study and the overall health of the Roman Economy is less than secure.
First and foremost, the study at best, tests the silver production from Spain. While Spanish ores are important (even crucial), they were not unique to the excavation and smelting of silver in the Mediterranean, even in the Roman world, not necessarily of the economy as a whole. Best-case scenario, we can assume that Spanish smelting virtually stopped in the third century. Whether this assumption is correct or not I do not know.
Why this study is problematic, we need to investigate ideas about the Roman World and antiquity. The late-Republic was a disaster, the first and second century were great, the third was a time of crisis, a prelude to the decline and fall of the Roman Empire in the fourth and fifth century. The data correlates to this vision. But this does not mean that this is the truth. The third century was indeed a time of crisis, and this is, in appearance, noted in the coin record: emperors debased both the silver and the bronze coinage so that purity would plummet to ca. 5%. Nevertheless, this did not have the effects we would suspect:
1) The price record in the Egyptian papyri show that there was no inflation until the later third century, when purity would increase. This would mean that the mass of coin in circulation did not increase.
2) Test cases in Spain (Kulikowski 2006), Palmyra (As’Sadh and Yon 2001) show that there was sufficient wealth to increase building programs. Rome’s walls, once taken to be a marker of decline, still required funds to be paid.
3) Hoards of silver imperial coins also show that faith in the Imperial coinage did not wane (Kulikowski 2017).
So the study of McConnell et al. illustrates this decrease in silver production but its effects on crisis are less clear.
A second point of contention follows my area of expertise, namely Late Antiquity. The graph given shows that silver production did not increase in the fourth century, suggesting the economy did not pick up. We have seen, with the example of the third century that we need to be careful. This is even more true following the reforms of imperial coinage in the fourth century, first by Diocletian and then by Constantine. Put simply, both emperors reintroduced the Aureus, a gold denomination that eventually replaced the silver Antoninii. While silver currencies did not stop altogether, gold became the standard currency for the empire (Banaji 2002). It makes sense, therefore, that the silver did not “pick up” in the fourth century, and that the record becomes spottier for Late Antiquity. Recent studies have shown that, in Africa, the late-fourth and early-fifth century were a time of renewed economic growth.
There is, lastly, a methodological point to consider. The validity of the study currently hinges on the fact that we can map events onto this graph. The graph alone does not say anything. The perception of decline in the third century, the perception of fall in the fourth and fifth gives the work credence. Moreover, this methodology is not fundamentally new: McCormick, in 2007, used climate data to highlight the fiscal policy of Carolingian kings in the eighth century.
To provide a brief conclusion: the study of ice core WILL yield important data. What these are, we do not know. Indeed, a lot more work needs to be done on the Roman economy, the relationship between imperial coinage and local currencies is still widely unknown. To what extent does economic behavior differ from modern days? It was, for instance, significantly harder for a Persian merchant to sell Chinese silk anywhere BUT the Mediterranean than an Iranian selling the same product today (market elasticity is also something to consider). Sourcing of emeralds using chemical and atomic compositions of individual mines (research conducted in part by Gaston Giuliani and, by Kris Lanefor Latin America) will also be important for future research on the economy. Anthropologists have shown that economy depended largely on knowledge of existing markets and finding new production sources, not necessarily finding new markets. The flow of goods was far less flexible then than it is today. All that to say that the silver production of the Spanish mines is not indicative of the state of Mediterranean economy.
