The Roman Empire collapsed because the climate changed in the 5th century.e century. The cooling favored the development of germs and devastating pandemics, which cannot, however, be understood without looking at Roman globalization and the circulation of products and people.
With this work published in Princeton in 2017 and quickly translated into French, Kyle Harper, professor at the University of Oklahoma, is part of the long tradition that, since Gibbon, has considered the disappearance of the Roman Empire to be a major problem in the history of humanity. The originality of his approach and the chronology chosen make it an important work not only for those who wonder about this question, but also for readers who would like to discover the richness and complexity of Late Antiquity, too long considered the decadent counterpart of the brilliant Early Roman Empire. It is also a book that allows us to take the measure of the historiographical renewals opened up by progress in climate sciences and genetics. The book opens with a remarkable preface by Benoît Rossignol, who places the work in the context of current scientific developments and historiographical issues.
A History of Epidemics in the Roman Empire
Indeed, the author intends to open the immense “archive storehouse”, according to Benoît Rossignol’s formula, that these sciences are currently constituting. He shows a historical discipline in full renewal: the possibility of cross-referencing literary sources on climatic phenomena with scientific measurements, or of analyzing the genetic material of the killer germs of antiquity, opens up exciting perspectives that, without a doubt, will experience great development in the years to come if the decompartmentalization between these disciplines, academically so distant from each other, continues. The political chronology, without being ignored, is thus confronted with that of the climatic changes that affected the Roman Empire and which, among other effects, favored the development of devastating epidemics.
From the Antonine plague in the 160s to that of Justinian in the mid-18th century, VIe century, passing through that known as that of Cyprian, which occurs in the heart of the “crisis of IIIe century” whose complexity is here remarkably presented, the author shows the weight of climatic and epidemic elements in the history of the Roman Empire, avoiding, most of the time, but not always, making them the sole cause of political and social developments. The work oscillates between a rigorous scientific presentation, which highlights the complex interaction between human societies and natural elements, and a sometimes catastrophic vision which simplifies the subject. The end of the book, in particular, tends to attribute the religious developments of the end of Antiquity to the sole feeling of disarray caused by the Little Ice Age of the end of Antiquity and the great plague of Justinian.
Certainly, the effects of these two elements were extremely devastating: the “year without a summer” of 536, which inaugurated the coldest decade in the history of Europe for 2000 years, had dramatic consequences on the harvests, and the plague that followed it a few years later killed perhaps half the population of the affected regions. Indeed, this serious pandemic began during the cold decade of 530-540 (the link between this climatic phenomenon and the spread of the plague is not clear) and, starting from Pelusium in Egypt, it spread throughout the Mediterranean area. In Constantinople, in the spring of 542, John of Ephesus and Procopius of Caesarea describe the daily accumulation of thousands of corpses: 250,000 to 300,000 people are said to have died, for a population estimated at half a million inhabitants.
The book has the merit of linking the philosophical and religious atmosphere of the middle of the VIe century to these distressing phenomena in the face of which contemporaries were totally powerless. Should we go so far as to write that the plague of Justinian was “the most disastrous event in the entire history of humanity to date” (p. 347)?
Nature, the driving force of history?
One can regret that the author thus too often gives in to the shock formula and that the style suffers from a certain heaviness, which the translation does not manage to lighten, some passages remaining truly obscure. The whole contains repetitions that are sometimes tiresome, and the work would probably have gained from more concision. But these regrets remain minor in view of the richness of Kyle Harper’s work, which manages to make a story that is fundamentally very technical lively and accessible while embracing a period of four centuries.
“From a rat’s point of view, the Roman Empire was an unlikely blessing” (p. 289), the author writes, thus leading the reader to look away from the political struggles for imperial power to the economic and social functioning of the empire, and therefore its natural environment. Indeed, the apogee of the Roman world corresponds to a climatic optimum that was established around 250 BCE and whose end, in the second half of the IIe century, is one of the factors in the structural changes that gave rise to the world of late antiquity. The Little Ice Age that set in around 450 AD corresponds to the most difficult times, with in particular the breakup of the empire in the West. During the climatic optimum, Roman globalization and the economic integration of the provinces allowed the development of trade and a certain prosperity, but also the circulation of disease vectors; thanks to the cooling of the climate, in a troubled political context, pandemics took on a tragic dimension. Thus, the plague of Marcus Aurelius in the 160s – probably smallpox – was a serious but surmountable crisis. That of Cyprian, in the 250s, was more difficult to overcome for an empire beset by internal and external wars. And in the 540s, the empire of Justinian, whose population was already considerably weakened, did not recover from the pandemic: the plague of VIe century can be considered as a marker of the end of Antiquity.
The question raised by the book is therefore that of the weight of natural elements on human societies. The author tends to give “nature” the leading role, and the book resonates with contemporary issues on the effects of climate change, described as a superior force that would impose itself on a powerless humanity, and in the face of which all social classes would be equal. But the book itself provides many examples reminding us that “nature” is not a character external to human history who would come to brutally break empires. As the story of Justinian’s plague bacillus shows, the success of killer germs cannot be understood outside the social and economic structures of late antiquity: the very possibility of its emergence throughout the Mediterranean is the product of Roman globalization, in which products, men, and diseases circulate. We must not act “as if we were the only instrumentalists in the orchestra” (p. 81), writes Kyle Harper: according to him, the climate and germs are instrumentalists… or even the real conductors. The interest of such an approach, in the history of the last three centuries of the Roman Empire, is to reflect on the way in which the empire had to adapt to a significant change in natural conditions. But the risk, which the book does not always avoid, is to neglect the weight of conflicts and contradictions in the imperial system itself, in favor of a catastrophist approach – to believe that the human orchestra is a harmonious whole whose concert is sometimes stopped by the limits imposed by nature, in a neo-Malthusian vision partially assumed by the author in the last chapter.
Kyle Harper is fortunately much more nuanced in his story than some of his formulas might lead one to believe. He is particularly good at teaching in his account of the Justinian plague, to help us understand how the bacteria Yersinia Pestisafter having long been originally a rodent disease “lurking in burrows in central Asia” (p. 301), became a serial killer thanks to the movements of black rats and their fleas throughout the Roman world. This is indeed the conjunction of genetic mutations in the bacteria Yersinia Pestisof a well-established Mediterranean trade which allowed the circulation of cereals, but also that of animals carrying diseases, of a sudden climate change in the 530s, and of the instability of the empire under Justinian, which explains the severity of the first pandemic in human history.