While I am certainly very grateful to the team of authors of Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity, it is curious that the only quantitative part of their study was coming up with the lead pollution curve. All the comparisons between the lead curve and historical events in Rome and elsewhere in the Western Mediterranean were entirely qualitative. Yet the greatest strength of employing quantitative proxies results when we examine different proxies against each other.
In this second installment of the series (first installment here) I will compare the lead curve to a quantitative measure of building activity in Rome. I will focus on religious buildings (pagan temples and Christian churches), because they typically represent a substantial investment of resources and because they can be often accurately dated. I have used this building index in several case studies described in Secular Cycles. For this post, the list of temples was taken from Richardson, L. 1992. A new topographical dictionary of ancient Rome. Johns Hopkins University Press, Baltimore; and churches are from Ward-Perkins, B. 1984. From Classical Antiquity to the Middle Ages: Urban public building in northern and central Italy, AD 300-850. Oxford University Press, Oxford.
Here I plot these data in two ways:
The tan vertical bars tell us how many temples (or churches) were built in Rome in each decade. The thick brown curve smooths over short-term fluctuations, helping us to visualize longer (secular) dynamics. As we see, the curve generally traces out the four secular cycles in Roman history. One partial exception is the building activity gap in the middle of the first century, which divides the Principate cycle into two phases. One possible explanation of this interruption is that there was a short-lived outbreak of internal violence during the first century (the deposition of Emperor Nero followed by the Year of the Four Emperors).
Now let’s plot the building curve against the lead pollution curve:
What we see is that there is a lot of difference in detail. But there are also shared features. The secular cycles in both curves tend to have peaks and troughs at roughly similar times (except for the “double-headed” Principate cycle in the building data). Additionally, the overall heights of each secular peak are similar in the two curves. The overall correlation coefficient is a respectable 0.62. This is not a bad result, considering that the two curves were derived using completely different methodologies, and that they reflect very different socio-economic processes. On top of that, the first cycle in the pollution curve is not even due to Rome, since the mines during the early period were operated by the Carthaginians.