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How pandemics extinguished the Roman empire

What the fall of Rome teaches us about the twin threats of lethal disease and ecological disaster.

At their peak during the reign of Trajan, around the start of the second century AD, the Romans had governed distant regions of the globe for longer than any other pre-modern state. The empire’s borders stretched across the Rhine, the Danube, the Euphrates, the edge of the Sahara and northern Britain. By the time of Pope Gregory the Great (c540-604), the Roman colossus had become a Byzantine outpost ruling a few scattered territories from Constantinople. With the breakdown of the Roman order western Europe fragmented into warring Germanic kingdoms while Islamic armies conquered much of what remained of the empire. Housing around one million people in the first century AD, Rome was reduced to around 20,000 inhabitants.

As Kyle Harper writes, the fall of Rome may have been “the single greatest regression in all of human history”. In 1984, he tells us, a German classicist catalogued more than 200 explanations of this regression. Military over-reach, increasing reliance on slave labour, excessive spending and taxation to pay for a decadent diet of “bread and circuses”, and the rise of Christianity have been cited. Rome did not fall in a day, and no doubt these and other factors featured in a long process of decline. But all of these standard accounts put human agency at the heart of the story, when the deciding forces may not have been human at all. Instead, Harper argues compellingly, it was pandemic diseases amplified by shifts in the climate that unravelled the global networks of connectivity the Romans had constructed over centuries. As he puts it, “The ecology of the empire had built an infrastructure awaiting a pandemic.”

Among the casualties of the Roman collapse was a classical view of the world. In Stoicism – a system of thought widespread among Roman aristocrats and administrators, and embodied in the philosopher-emperor Marcus Aurelius (121-180) – wisdom was achieved by identifying oneself with an unchanging natural order. In this view there could be no new evils: no novel diseases, for example, for which a wise humanity would be unprepared. A virtuous civilised way of life could be achieved and preserved by emulating a rational and harmonious cosmos.

A succession of pandemics shattered this classical world-view. The Antonine Plague began in 165 and peaked around 180, when witnesses reported as many as 2,000 people dying in Rome every day and mortality throughout the empire ran into millions. Overall, Harper estimates, around seven million people may have perished during this pandemic. Struggling to make sense of this catastrophe, which mocked his faith in a rational cosmos, Aurelius fell back in his Meditations on the Stoic practice of trying to live each day as his last.

In the mid-third century Rome was shaken by the Plague of Cyprian, whose nature is still obscure. By the time of Gregory and the catastrophic Justinian plague – a bubonic pandemic like the medieval Black Death – the natural world had come to be seen as chaotic and antagonistic to humankind. The result was a febrile cult of the god Apollo, while Christianity received a boost without which it might not have gone on to be adopted as the failing empire’s state religion.

As Harper makes clear, the altered perception of the natural world that accompanied the fall of Rome reflected changing environmental realities. The planet’s ecology was no more stable in the ancient world than it is today. The Romans themselves had changed it:

By its nature, Roman civilisation seemed to unlock the pestilential potential of the landscape. The expansion of agriculture brought civilisation deeper into habitats friendly with the mosquito. Deforestation facilitated the pooling of water and turned the forbidding forest into fields where mosquitos more easily multiplied… The Romans were environmental engineers extraordinaire.

Yet shifts in climate were not, in Roman times, primarily anthropogenic in origin: “Climate change was always an exogenous factor, a true wild card transcending all the other rules of the game. From without, it reshaped the demographic and agrarian foundations of life, upon which the more elaborate structures of society and the state depended.” Small changes in the path of the Earth, together with slight variations in its tilt and spin, changed the planetary climate in lasting ways. During the Pleistocene era there were long periods of icy cold, and it was only when the planet entered the warm and wet Holocene around 12,000 years ago that complex and extended societies and forms of government could develop. Even then, solar activity interacted with the Earth’s inherently variable climate to disrupt the pattern of human life. Violent eruptions during the reign of Justinian produced a colder period – the Late Antique Little Ice Age – that lasted for around 150 years. The cycle of the seasons was disturbed and crops failed. Overall, though, the Romans were lucky. Their empire reached its maximal extent during a period of relative stability called the Roman Climate Optimum.

Human agency was at work in the fall of Rome through the unintended consequences of the near-global connectivity the empire embodied. Infection entered Rome via far-flung trade networks and flea-ridden rodent populations that thrived in grain stores. With human numbers higher than ever before, large populations were crowded together in cities. Tuberculosis, leprosy and a formidable array of fevers were endemic. The vast reach of Roman power exposed these vulnerable populations to infections from the furthest reaches of the Earth. The Roman plagues were a by-product of an early experiment in globalisation. The possibility, and eventual inevitability, of pandemics was wired into the structures of imperial Rome at the height of its power.

Rome was defeated by natural causes, but it did not fall because of a scarcity of natural resources. Deploying ruthless force, technological ingenuity and high levels of political skill, the empire escaped the supposedly iron laws of population laid down by Thomas Malthus in the 18th century. It was not an inability to feed itself that felled the Roman colossus. A subtler Malthusian dynamic was in play. “The dense urban habitats, the unflinching transformation of landscapes, the strong networks of connectivity within – and especially beyond – the empire, all contributed to a unique microbial environment.” The very achievements of Roman civilisation contained the conditions for its collapse. The far-reaching interconnectedness that the Roman empire secured made it intrinsically fragile. By constructing the closest approximation to date of a universal order, the Romans created ideal conditions for the plagues that would overwhelm it.

A professor of classics and letters, and the senior vice-president and provost at the University of Oklahoma, Harper has given us a book that will be of urgent interest to readers struggling to adjust to a disruption in their experience unlike any they have known. But the value of his book (first published in 2017) does not depend on this grim coincidence. However the current pandemic unfolds, this revelatory successor to Edward Gibbon’s Decline and Fall of the Roman Empire (1776) presents an interpretation of one of history’s turning points that is mind-opening and salutary.

A key theme in Harper’s story is that the collapse of Roman civilisation could not have been avoided by greater sagacity. When they built their grand edifice the Romans could not have known that they were also creating an environment in which diseases could spread as never before, and they had no understanding of the climate changes that were under way. Still less could they have known that a conjunction of the two would lead to the destruction of their world. It is hardly surprising that by the time of Gregory, the Roman mind was unhinged by eschatological fears and apocalyptic religions.

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The world in which Covid-19 emerged is too different from that of the Romans for any exact parallels to be possible. Much is known about climate change, including the fact that its current wave is predominantly man-made. Virology is an advancing science, and a vaccine is a realistic prospect. Conceivably, Covid-19 may not turn out to be as deadly as some earlier viruses. It could even disappear, as did Sars in 2002-04. But there appears to be little scientific evidence for these speculative possibilities, and basing policies on them would be reckless in the extreme.

The more fundamental point is that the future behaviour of the virus is unknown. Different statistical models produce divergent trajectories for its spread and lethality. Science is an area of human activity in which the steady growth of knowledge is a demonstrable reality. But scientific inquiry cannot eliminate uncertainty regarding the future, or the impact this uncertainty has on the mind when human well-being is seriously at risk. In this regard and others, we may be closer to the Romans than we like to think.

There are undeniable similarities. It is not only that Covid-19 appeared during a time of peak globalisation, with tightly stretched supply chains that had little resilience to shocks. The virus has also emerged against a background of large-scale environmental engineering. In an ominous twist of the Malthusian dynamic, humans are expanding into and swiftly degrading regions such as the Amazon that were previously lightly inhabited by hunter-gatherers. As these areas are turned over to agriculture, local ecologies are severely disturbed. Wilderness is fast vanishing, and as it retreats animal-borne infections jump more easily to humans. Population growth gives this process a powerful momentum. As Harper writes, “The growth of human numbers has… rewritten the rules of the game for the microbial co-residents of the planet Earth.” Mass air-travel accelerates disease transmission from wildlife markets and factory farms. Like ancient Rome, the pre-Covid global order was wired for pandemic.

It is the impact of the virus on prevailing belief systems that suggests the most intriguing parallels. Just as the combination of climate change with pandemics undermined a ruling classical world-view, the virus has shaken the modern faith that humankind can reshape the natural world as it pleases. The very idea of nature as an insuperable constraint on human ambitions has become heretical. For many, it seems, nothing really exists apart from human thoughts and feelings. Serving no human purpose, the virus is a deadly threat to this solipsistic modern faith. As Harper writes:

There are maybe a trillion microbial species in total; the average human lumbers around bearing 40 trillion bacterial cells alone. They have been here for some three and a half billion years. It’s a microbe’s world – we’re just living in it.

It was only to be expected that views of the world would mutate with the arrival of the pandemic. Given the abrupt and drastic alteration in everyday experience it has brought, things could scarcely be otherwise. But the result has not been any greater realism in thinking. Undermining an established narrative of human advance, the pandemic has revealed and catalysed deep conflicts. Geopolitical rivalries are intensifying and xenophobia is being weaponised. In what used to be called the liberal West, intellectual tribalism and volatile ideologies thrive while conspiracy theories abound, along with fake news and quack cures. Political conflicts and cultural wars are being fought out with passionate intensity, while the virus – a lethal reminder of the brute reality of the unruly material world – spreads regardless of human beliefs.


All together now: thousands gather in Times Square, New York for a Black Lives Matter protest, 7 June. Credit: Michael Nigro/Pacific Press/Lightrocket 

As a result of the unequal costs of lockdown, government failures and demagogic manipulation, divisions within societies have sharpened. Initial solidarity in face of the pandemic has fractured. Compliance with social distancing is fraying and in some contexts breaking down. Protests against the public murder by police of an unarmed African American are justified by the intolerable racism that fuelled the killing. However, the virus does not care whether mass gatherings are peaceful or violent, composed of anti-racists or white supremacists, opportunistic looters or Cheltenham race-goers. Nor does it attach any significance to the fact that black people and other minorities are far more likely to be killed by it than the rest of the population. For the virus, all sections of society are targets and all mass gatherings super-spreader events.

Here, early-20th-century history sounds a note of warning. On 28 September 1918, while the First World War was still under way and the influenza epidemic seemed to be fading, the city of Philadelphia staged a grand parade to support the war effort. Around 200,000 people crowded together in Broad Street to cheer the marchers, and among them were some infected by the flu virus. On 3 October, municipal authorities locked down the city. By 5 October, around 2,600 people had died, and a week later the figure topped 4,500. Over a six-month period as many as 20,000 died of flu in the city. There must have been dozens, possibly hundreds of such mass gatherings in the US and other countries over the past few weeks. Some have observed degrees of social distancing, and Covid-19 is not flu. Even so, the risks are plain.

The pandemic has no pre-ordained trajectory, and because of our vastly superior medical resources is very unlikely to follow the catastrophic path of its predecessors in Roman times. Instead it poses a question. Human knowledge has increased tremendously, but are we so much more reasonable than the Romans were at their peak? Or are we descending into a state of collective derangement, far more rapidly than they did? The answer may begin to be clear over the coming months. 

The Fate of Rome: Climate, Disease and the End of an Empire
Kyle Harper
Princeton University Press, 440pp, £15.99

John Gray is the New Statesman’s lead book reviewer. His latest book is The Soul of the Marionette: A Short Enquiry into Human Freedom.

This article appears in the 19 June 2020 issue of the New Statesman, The History Wars