An interview with Kyle Harper, author of The Fate of Rome: Climate, Disease, and the End of an Empire
What is the fall of the Roman Empire?
The fall of the Roman Empire is one of the most dramatic episodes of political dissolution in the history of civilization—the long process that saw the fragmentation and disappearance of central Roman authority around the Mediterranean. In the second century, the Roman Empire was the world’s dominant superpower. One in four people on earth lived inside its borders. There was peace and prosperity on a scale never before seen. Five centuries later, Germanic kingdoms had conquered most of the west, and the Islamic caliphate was triumphant in most of the east. Population fell by maybe half, and there was less wealth, less trade, cruder institutions, and technological regression. The “fall of the empire” is a shorthand for all of the events and processes that led an empire that seemed invincible in the second century into a state of disintegration by A.D. 650.
What caused the empire to fall?
Historians have offered more than 200 answers, and obviously there was no single cause. But I argue that we have to allow environmental change—climate change and pathogen evolution—a dominant role. Human societies are deeply dependent upon their physical and biological environments, and these environments are radically unstable. The earth’s climate system has experienced significant climate change, even in the relatively stable epoch we know as the Holocene. And the biological environment—the set of organisms we share the planet with—has been wildly in flux, in ways that have redirected the course of human history. The empire was an intricate machine that depended on demographic and economic foundations, which fueled the army and the fiscal system. The Romans built their empire—unbeknownst to them—under unusually favorable climatic conditions. In a sense, their luck started to run out in the middle of the second century, with a sequence of climate change and new kinds of disease. Of course, these challenges did not spell the end of the empire. But the new reality became a part of the ongoing struggle to maintain their political dominance. Ultimately, the catastrophic pandemics that Rome suffered undermined the stability of the imperial machine.
How does new evidence change our answers to old questions?
Historians are the great unintended beneficiaries of at least two exciting new kinds of information about the past coming from the natural sciences. First, paleoclimate data. The need to understand global warming, and the earth’s climate system in general, has produced a treasure trove of new insights into the climate experienced by our ancestors. Two, genomic data. Thanks to the affordability of genome sequencing, we are learning a stunning amount about the story of the great killers of the past. The history of the bacterium that causes bubonic plague, Yersinia pestis, has really started to come into focus. It is a relatively young pathogen that evolved in central Asia and caused three great historical pandemics, the first of which afflicted the later Roman Empire in the reign of Justinian. This pandemic was probably as devastating as the medieval Black Death, carrying off something like half of the entire population. And, now, its genetic traces have been found in graves of the sixth century. What is most exciting, however, is the consilience—the leaping together—of new kinds of evidence and more traditional historical sources. I hasten to add that we historians are constantly finding new texts and documents and producing better understanding of old texts and documents. The ongoing, humanistic study of the Roman Empire is just as important as the thrilling scientific evidence. The pieces are starting to fit together.
How did diseases affect the course of Roman history?
All underdeveloped societies bore a heavy burden of infectious disease. Most deaths in the Roman world were caused by infectious disease. And the very success of the Roman Empire, paradoxically, exacerbated the endemic disease burden. The Romans were unhealthy. The dense urban habitats were unsanitary environments where low-level gastroenteric diseases were rampant. The transformation of the physical landscape facilitated the spread of mosquito-borne pathogens like malaria. The interconnection of the empire created a unified ‘disease pool’ where chronic diseases like tuberculosis and leprosy spread further than ever before. But, above all, the empire—and its massive trade contacts beyond the borders—opened the gate for newly evolved diseases, like smallpox, bubonic plague, measles, and possibly others—to enter the Roman world. The evolution of new, acute, directly communicable diseases created disease events—what are properly called pandemics—of a magnitude that had never been seen before. Three pandemics in particular—the Antonine Plague, the Plague of Cyprian, and above all the Justinianic Plague—shook the foundations of the Roman Empire.
Does the argument that “the environment did it” reduce the role of human factors?
There is simply no compelling way to describe the fall of the Roman Empire without an enormous allowance for human factors. The Empire was a human creation. Its fate was shaped by human choices and human structures. But I argue that we can actually understand the human element more deeply, and more sympathetically, with a deeper knowledge of the environmental dimensions of Roman history. The Romans were far from helpless victims of environmental catastrophe. They harnessed the power of the environment. They reshaped the disease ecology of the empire, with unintended consequences. They were resilient in the face of stress and strain. But we should not shy away from recognizing the power of nature. The physical and biological environment is an integral part of human life. There is really no separating human and natural factors in the story of Roman civilization.
What lessons can we learn from the fall of the Roman Empire?
The Romans have always captivated the imagination. The empire they built was truly extraordinary, in its scale and longevity and in the ways that its precocious development presaged modernity. And the dissolution of this empire has always been a poignant theme for reflecting on how even the greatest and most powerful of human constructions are ultimately transient. To be sure, our world is very different from the ancient world. We live long lives thanks to germ theory, public health, and antibiotic pharmaceuticals. Anthropogenic climate change is a greater risk than solar variability or volcanic winters. Still, we learn from the past because history is a humanistic discipline. We study the past and in the process emerge with a deeper, richer sense of what it means to be human. I hope that The Fate of Rome leaves its readers with a new sensibility toward the relationship between humanity and the environment. We care about the Romans because their civilization seemed to break free of some of the constraints that nature had imposed. But nature is cunning. Germs evolve. Surprises and paradox lurk in the heart of progress. The deep power of evolution can change the world in a mere moment. I hope the book sensitizes us to the awesome power of nature at all scales, from the microscopic to the global.
How did you decide to write a book on Rome and the environment?
I’ve wanted to write this book for a long time. I’ve been very fortunate to be around extremely creative people, including Michael McCormick, who was one of the first historians to insist that people in a traditionally humanistic field should pay attention to things like climate science, archaeological genetics, and bioanthropology. But only in the last couple of years has it even become possible to start pulling all the evidence together. The sequencing of the ancient genome of Yersinia pestis, for instance, is a watershed, as is the much clearer definition of the “late antique little ice age” achieved from tree rings and ice cores. All of this has happened in the last few years, and for those of us studying Roman history, it’s unbelievably fortunate. I think my book is the first to try to tie all this together with a robust model of how the Roman Empire actually worked, and what’s exciting is that over the next decade there will be lots of new evidence and plenty of revision to the story that I tell.
I also am lucky to be a Provost at the same time I’ve been working on this book. It means that I get to interact with atmospheric scientists, anthropologists, ecologists, microbiologists, and so on, on a daily basis. I have very generous colleagues who have helped me trespass across other disciplines. In turn, I hope my book shows why history is so valuable and so essential to other fields. Historians have a part to play in helping us understand everything from the landscape of global health to the chemistry of the atmosphere. In short, just as the natural sciences can help us understand human history better, so too can a deeper knowledge of the history of our species help us understand the natural world.