That is beginning to change. Scientific advances of the past two decades have shed new, empirical light on conditions such as climate changes and disease in long-gone eras: findings that are radically altering the way historians understand both distant cultures and the way history is made.
Kyle Harper’s The Fate of Rome: Climate, Disease, and the End of an Empire is an ambitious and convincing reappraisal of one of the most studied episodes of decline and fall in human history: how ancient Rome slowly collapsed, taking the project of human civilization back several leaps. This isn’t virgin territory: Harper references work by a small army of peers, not to mention extensive scientific studies and legendary tomes such as William H. McNeill’s Plagues and Peoples. Nonetheless, The Fate of Rome constitutes the most comprehensive reckoning to date of the nonhuman forces at play in the fall of the empire.
In brief: Microbiologists have now fleshed out the scattered and subjective primary accounts of disease in the Roman Empire, helping historians to fathom the true impact of the Antonine Plague of AD 165–180, which we now know was likely a smallpox outbreak; the Plague of Cyprian in the third century, which could have been Ebola; and even more apocalyptically, the Justinianic Plague that began in AD 541, a devastating pandemic we now know to have been bubonic plague, newly arrived in the Roman Empire. Harper estimates the mortality rate of the Justinianic Plague at around 50 percent, and notes that bubonic plague continued to attack the empire for two more centuries after 541, riding on the empire’s rats and recurring in humans whenever environmental conditions conspired: some 38 times over the next 200 years. The halving of the population in 541, followed by these periodic aftershocks, sent every sphere of public life into disarray, notably decimating the army and wreaking economic chaos. “[T]here is a relatively uncomplicated line from demographic collapse to the failure of the eastern empire,” writes Harper.
And we now know that the arrival of bubonic plague in the Roman Empire also coincided almost exactly with what has, in recent years, come to be known as the Late Antique Little Ice Age. Ice core records and tree-ring evidence show us that 536 AD — the “year without a summer” — opened both the coldest decade in the last two thousand years and a more prolonged cold snap lasting 125 years. The Late Antique Little Ice Age began with two enormous volcanic explosions that belched sulfate aerosols into the atmosphere, blocking solar radiation. As Murphy’s law or its Roman equivalent would have it, this period also saw a decline in solar output as well as spreading aridification in North Africa and frequent flooding in Anatolia and Mesopotamia. Then-emperor Justinian embarked on a series of environmental engineering projects, building cisterns and aqueducts, moving riverbeds and reclaiming floodplains, all in an effort to safeguard his civilization. His efforts were futile: nature would not be mastered. By the end of the sixth century, after more than 40 years of misery wrought by climate and disease, Pope Gregory the Great was fully assured that the end times were come. “I sigh longingly for the remedy of death […] People arriving from the East describe worse desolations still. By all these things, as the end of the world draws near, you know that the affliction is general.”
What a contrast with the conditions under which the Roman Empire had first flourished. During the Roman Climate Optimum — some 350 years of unusually warm, moist, and disaster-free climate between around 200 BC and AD 150 — Rome began its rise to power. The people of the early Roman Empire had no idea how much they owed to this climate — much as we took the Holocene for granted in building our own empires of prosperity, in which by one estimate natural processes have accounted for 75 cents in every dollar produced. The Roman Climate Optimum would come to an end around AD 150, contributing to the Crisis of the Third Century. At the end of the fourth century, a terrible drought on the Eurasian Steppe turned the Huns into climate refugees, descending on the empire; the invasion gutted the Roman army and split the empire between east and west. And all this was small fry compared to the Little Ice Age still to come.
My division, here, into disease and climate factors does Harper’s work a disservice: he takes pains to show that no such separation exists. Rather, disease ecology, climate events, and human activity fed — and still feed — on each other in an endless cycle. Had the Romans not excelled at trade and exploration, they wouldn’t have brought bubonic plague to the empire from Asia; had they not required such huge stores of grain to feed the population, the host rats wouldn’t have multiplied; had the climate not cooled so drastically, the population might have been better equipped to withstand the plague. And because human, disease, and climate factors are so inextricably linked, Harper shows that this new reading doesn’t usurp the traditional explanations for Rome’s fall but rather fleshes them out. With this background filled in, it’s easier to understand the empire’s susceptibility to invasion, economic troubles, and internal division.
Harper’s purpose, then, is not to deny humankind’s agency but rather to contextualize it as a force, and sometimes a powerful one, within the infinitely complex system of forces that is life on Earth. The Fate of Rome is unapologetically a work of scholarly history, and as such Harper doesn’t insist at length on the parallels with our own age. Non-specialized readers will nevertheless be galvanized by the book’s meticulous examination of how catastrophes, unfolding slowly but inexorably, blight advanced cultures, particularly when those cultures habitually meddle with and underestimate nature. The work might even serve as a reminder that humans are, in fact, not antagonists or caretakers of nature — or “great men” who could hold back a hurricane if they only delivered the right speech — but rather wholly, helplessly, and before all else a part of it, with no chance ever of extricating ourselves from its web.