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How Climate Change and Plague Helped Bring Down the Roman Empire

We can learn crucial lessons by examining the natural forces that shaped Rome’s rise and fall

Thomas Cole's The Course of Empire: Desolation, 1836 (Courtesy New York Historical Society/Wikipedia)



In the middle of the second century, the Romans controlled a huge, geographically diverse part of the globe, from northern Britain to the edges of the Sahara, from the Atlantic to Mesopotamia. The generally prosperous population peaked at 75 million. Eventually, all free inhabitants of the empire came to enjoy the rights of Roman citizenship. Little wonder that the 18th-century English historian Edward Gibbon judged this age the ‘most happy’ in the history of our speciesyet today we are more likely to see the advance of Roman civilization as unwittingly planting the seeds of its own demise.

Five centuries later, the Roman empire was a small Byzantine rump-state controlled from Constantinople, its near-eastern provinces lost to Islamic invasions, its western lands covered by a patchwork of Germanic kingdoms. Trade receded, cities shrank and technological advance halted. Despite the cultural vitality and spiritual legacy of these centuries, this period was marked by a declining population, political fragmentation and lower levels of material complexity. When the historian Ian Morris at Stanford University created a universal social-development index, the fall of Rome emerged as the greatest setback in the history of human civilization. 




It turns out that climate had a major role in the rise and fall of Roman civilization. The empire-builders benefitted from impeccable timing: the characteristic warm, wet and stable weather was conducive to economic productivity in an agrarian society. The benefits of economic growth supported the political and social bargains by which the Roman empire controlled its vast territory. The favorable climate, in ways subtle and profound, was baked into the empire’s innermost structure.

The end of this lucky climate regime did not immediately, or in any simple deterministic sense, spell the doom of Rome. Rather, a less favorable climate undermined its power just when the empire was imperilled by more dangerous enemiesGermans, Persiansfrom without. Climate instability peaked in the sixth century, during the reign of Justinian. Work by dendro-chronologists and ice-core experts points to an enormous spasm of volcanic activity in the 530s and 540s CE, unlike anything else in the past few thousand years. This violent sequence of eruptions triggered what is now called the ‘Late Antique Little Ice Age,’ when much colder temperatures endured for at least 150 years.






Though it rebounded, the empire was profoundly alteredwith a new kind of emperor, a new kind of money, a new kind of society, and soon a new religion known as Christianity. Most dramatically, in the sixth century a resurgent empire led by Justinian faced a pandemic of bubonic plague, a prelude to the medieval Black Death. The toll was unfathomablemaybe half the population was felled.



The plague pandemic was an event of astonishing ecological complexity. It required purely chance conjunctions, especially if the initial outbreak beyond the reservoir rodents in central Asia was triggered by those massive volcanic eruptions in the years preceding it. It also involved the unintended consequences of the built human environmentsuch as the global trade networks that shuttled the germ onto Roman shores, or the proliferation of rats inside the empire.

The pandemic baffles our distinctions between structure and chance, pattern and contingency. Therein lies one of the lessons of Rome. Humans shape natureabove all, the ecological conditions within which evolution plays out. But nature remains blind to our intentions, and other organisms and ecosystems do not obey our rules. Climate change and disease evolution have been the wild cards of human history.


Perhaps we could come to see the Romans not so much as an ancient civilization, standing across an impassable divide from our modern age, but rather as the makers of our world today. They built a civilization where global networks, emerging infectious diseases and ecological instability were decisive forces in the fate of human societies. The Romans, too, thought they had the upper hand over the fickle and furious power of the natural environment.

History warns us: they were wrong.Aeon counter – do not remove

Kyle Harper is a professor of classics and letters and senior vice president and provost at the University of Oklahoma. His latest book is The Fate of Rome: Climate, Disease, and the End of an Empire (2017).


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