The Fate of Rome

Climate, Disease, and the End of an Empire

Kyle Harper

• Publisher: Princeton University Press
• Year: 2017
• ISBN:
  9781400888917
• Topic: History
• Subtopic: Roman Ancient History
• Index: History

How devastating viruses, pandemics, and other natural catastrophes swept through the far-flung Roman Empire and helped to bring down one of the mightiest civilizations of the ancient world Here is the monumental retelling of one of the most consequential chapters of human history: the fall of the Roman Empire. The Fate of Rome is the first book to examine the catastrophic role that climate change and infectious diseases played in the collapse of Rome's power—a story of nature's triumph over human ambition.Interweaving a grand historical narrative with cutting-edge climate science and genetic discoveries, Kyle Harper traces how the fate of Rome was decided not just by emperors, soldiers, and barbarians but also by volcanic eruptions, solar cycles, climate instability, and devastating viruses and bacteria. He takes readers from Rome's pinnacle in the second century, when the empire seemed an invincible superpower, to its unraveling by the seventh century, when Rome was politically fragmented and materially depleted. Harper describes how the Romans were resilient in the face of enormous environmental stress, until the besieged empire could no longer withstand the combined challenges of a "little ice age" and recurrent outbreaks of bubonic plague.A poignant reflection on humanity's intimate relationship with the environment, The Fate of Rome provides a sweeping account of how one of history's greatest civilizations encountered and endured, yet ultimately succumbed to the cumulative burden of nature's violence. The example of Rome is a timely reminder that climate change and germ evolution have shaped the world we inhabit—in ways that are surprising and profound.

Environment and Empire

THE SHAPE OF THE ROMAN EMPIRE

Rome’s rise is a story with the capacity to astonish us, all the more so since the Romans were relative latecomers to the power politics of the Mediterranean. By established convention, Rome’s ancient history is divided into three epochs: the monarchy, the republic, and the empire. The centuries of monarchy are lost in the fog of time, remembered only in fabulous origins myths that told later Romans how they came to be. Archaeologists have found the debris of at least transient human presence around Rome going back to the Bronze Age, in the second millennium BC. The Romans themselves dated their city’s founding and the reign of their first king, Romulus, to the middle of the eighth century BC. Indeed, not far from where Claudian stood in the forum, beneath all the brick and marble, there had once been nothing more than a humble agglomeration of wooden huts. This hamlet could not have seemed especially propitious at the time.¹

For centuries, Rome stood in the shadow of her Etruscan neighbors. The Etruscans in turn were outclassed by the political experiments underway to the east and south. The early classical Mediterranean belonged to the Greeks and Phoenicians. While Rome was still a village of letterless cattle rustlers, the Greeks were writing epic and lyric poetry, experimenting with democracy, and inventing drama, philosophy, and history as we know them. On nearer shores, the Punic peoples of Carthage built an ambitious empire, before the Romans knew how to rig a sail. Fifteen miles inland, along the soggy banks of the Tiber River, Rome was a backwater, a spectator to the creativity of the early classical world.²

Around 509 BC the Romans shuffled off their kings and inaugurated the republic. Now they gradually step into history. From the time they are known to us, Rome’s political and religious institutions were a blend of the indigenous and the adopted. The Romans were unabashed borrowers. Even the first code of Roman law, the Twelve Tables, was proudly confessed to be plagiarized from Athens. The Roman republic belongs among the many citizenship-based political experiments of the classical Mediterranean. But the Romans put their own accents on the idea of a quasi-egalitarian polity. Exceptional religious piety. Radical ideologies of civic sacrifice. Fanatical militarism. Legal and cultural mechanisms to incorporate former enemies as allies and citizens. And though the Romans themselves came to believe that they were promised imperium sine fine by the gods, there was nothing ineluctable about Rome’s destiny, no glaring geographical or technological secret of superiority. Only once in history did the city become the seat of a great empire.

Rome’s rise coincided with a period of geopolitical disorder in the wider Mediterranean in the last centuries before Christ. Republican institutions and militaristic values allowed the Romans to concentrate unprecedented state violence, at an opportune moment of history. The legions destroyed their rivals one by one. The building of the empire was bloody business. The war machine whetted its own appetite. Soldiers were settled in rectilinear Roman colonies, imposed by brute force all over the Mediterranean. In the last century of this age of unbridled conquest, grand Shakespearean characters bestride the stage of history. Not by accident is western historical consciousness so disproportionately concentrated in these last few generations of the republic. The making of Rome’s empire was not quite like anything that had happened before. Suddenly, levels of wealth and development lunged toward modernity, surpassing anything previously witnessed in the experience of our species. The teetering republican constitution generated profound reflections on the meaning of freedom, virtue, community. The acquisition of imperial power inspired enduring conversations about its proper exercise. Roman law helped to birth norms of governance, by which even the masters of empire might be held to account. But the scaling up of sheer power also fueled the cataclysmic civil violence that ushered in an age of autocracy. In the apt words of Mary Beard, “the empire created the emperors—not the other way round.”³

By the time Augustus (r. 27 BC–AD 14) brought the last meaningful stretches of the shore under Roman dominion, it was no idle boast to call the Mediterranean “mare nostrum,” our sea. To take full measure of the Roman accomplishment, and to understand the mechanics of ancient imperialism, we must know some basic facts about life in an ancient society. Life was slow, organic, fragile, and constrained. Time marched to the dull rhythms of foot and hoof. Waterways were the real circulatory system of the empire, but in the cold and stormy season the seas closed, and every town became an island. Energy was forbiddingly scarce. Human and animal muscle for force, timber and scrub for fuel. Life was lived close to the land. Eight in ten people lived outside of cities. Even the towns had a more rural character than we might imagine, made lively by the bleats and brays—and pungent smells—of their four-legged inhabitants. Survival depended on the delivery of rain in a precarious environment. For the vast majority, cereals dominated the diet. “Give us this day our daily bread” was a sincere petition. Death always loomed. Life expectancy at birth was in the 20s, probably the mid-20s, in a world where infectious disease raged promiscuously. All of these invisible constraints were as real as gravity, defining the laws of motion in the world the Romans knew.⁴

These limits cast into relief the sheer spatial achievement of the Roman Empire. Without telecommunications or motorized transport, the Romans built an empire connecting vastly different parts of the globe. The empire’s northern fingers reached across the 56^th parallel, while the southern edges dipped below 24° N. “Of all the contiguous empires in premodern history, only those of the Mongols, Incas, and Russian czars matched or exceeded the north-south range of Roman rule.” Few empires, and none so long-lived, grasped parts of the earth reaching from the upper mid-latitudes to the outskirts of the tropics.⁵

The northern and western parts of the empire were under the control of the Atlantic climate. At the ecological center of the empire was the Mediterranean. The delicate, moody features of the Mediterranean climate—arid summers and wet winters against a relatively temperate backdrop—make it a distinct type of climate. The dynamics of a giant, inland sea, combined with the knuckled texture of its inland terrains, pack extreme diversity into miniature scale. Along the empire’s southern and eastern edges, the high pressure of the subtropical atmosphere won out, turning the land into pre-desert and then true desert. And Egypt, the breadbasket of the empire, plugged the Romans into wholly other climate regimes: the life-bringing Nile floods originated in Ethiopian highlands watered by the monsoons. The Romans ruled all this.⁶

The Romans could not impose their will on so vast a territory by violence alone. The maintenance of the empire required economies of force and constant bargaining with those inside Roman boundaries and beyond. Over the course of the empire’s long life, the inner logic of imperial power, those economies and bargains, shifted shape many times.

Augustus gave order to the regime we recognize as the high Roman Empire. Augustus was a political genius, gifted with an uncannily long lifespan, who presided over the death throes of the republican constitution. During his reign, the campaigns of conquest, which had been fueled by elite competition for power in the late republican regime, started to slow. His reign was advertised as a time of peace. The gates to the Temple of Janus, which the Romans left open in times of war, had been closed twice in seven centuries. Augustus made a show of closing them three times. He demobilized the permanent citizen legions and replaced them with professional armies. The late republic had still been an age of gratuitous plunder. Slowly but surely, though, norms of governance and justice began to prevail in the conquered territories. Plunder was routinized, morphed into taxation. When resistance did flare, it was snuffed out with spectacular force, as in Judea and Britain. New citizens were made in the provinces, coming like a trickle at first, but subsequently faster and faster.

Map 2. Ecological Zones of the Roman Empire

The grand and decisive imperial bargain, which defined the imperial regime in the first two centuries, was the implicit accord between the empire and “the cities.” The Romans ruled through cities and their noble families. The Romans coaxed the civic aristocracies of the Mediterranean world into their imperial project. By leaving tax collection in the hands of the local gentry, and bestowing citizenship liberally, the Romans co-opted elites across three continents into the governing class and thereby managed to command a vast empire with only a few hundred high-ranking Roman officials. In retrospect, it is surprising how quickly the empire ceased to be a mechanism of naked extraction, and became a sort of commonwealth.⁷

The durability of the empire depended on the grand bargain. It was a gambit, and it worked. In the course of the pax Romana, as predation turned to governance, the empire and its many peoples flourished. It started with population. In the most uncomplicated sense, people multiplied. There had never been so many people. Cities spilled beyond their accustomed limits. The settled landscape thickened. New fields were cut from the forests. Farms crept up the hillsides. Everything organic seemed to thrive in the sunshine of the Roman Empire. Sometime around the first century of this era, the population of Rome itself probably topped one million inhabitants, the first city to do so, and the only western one until London circa 1800. At the peak in the middle of the second century, some seventy-five million people in all came under Roman sway, a quarter of the globe’s total population.⁸

In a slow-moving society, such insistent growth—on this scale, over this arc of time—can easily spell doom. Land is the principal factor of production, and it is stubbornly finite. As the population soared, people should have been pushed onto ever more marginal land, harder and harder pressed to extract energy from the environment. Thomas Malthus well understood the intrinsic and paradoxical relationships between human societies and their food supplies. “The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race. The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction, and often finish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague advance in terrific array, and sweep off their thousands and tens of thousands. Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow levels the population with the food of the world.”⁹

Yet . . . the Romans manifestly did not succumb to mass-scale starvation. Herein is to be found the hidden logic of the empire’s success. Far from steadily sinking into misery, the Romans achieved per capita economic growth, straight into the teeth of headlong demographic expansion. The empire was able to defy, or at least defer, the grim logic of Malthusian pressure.

In the modern world, we are accustomed to annual growth rates of 2–3 percent, on which our hopes and pension plans depend. It was not so in ancient times. By their nature, pre-industrial economies were on a tight energy leash, constrained in their ability to extract and exchange energy more efficiently on any sustainable basis. But premodern history was neither a slow, steady ascent toward modernity, nor the proverbial hockey stick—a flat-line of bleak subsistence until the singular energy breakthroughs of the Industrial Revolution. Rather, it was characterized by pulses of expansion and then disintegration. Jack Goldstone has proposed the term “efflorescence” for those phases of expansion, when background conditions conduce to real growth for some happy length of time. This growth can be extensive, as people multiply and more resources are turned to productive use, but as Malthus described, this kind of growth eventually runs out of room; more promisingly, growth can be intensive, when trade and technology are employed to extract energy more efficiently from the environment.¹⁰

The Roman Empire set the stage for an efflorescence of historic proportions. Already in the late republic, Italy experienced precocious leaps forward in social development. To a certain extent, the prosperity of Italy might be written off as the result of sheer takings, naked political rents seized as the fruits of conquest. But underneath this veneer of extracted wealth, real growth was afoot. This growth not only continued after the military expansion had reached its outer bounds—it now diffused throughout the conquered lands. The Romans did not merely rule territory, transferring some margin of surplus from periphery to center. The integration of the empire was catalytic. Slowly but steadily, Roman rule changed the face of the societies under its dominion. Commerce, markets, technology, urbanization: the empire and its many peoples seized the levers of development. For more than a century and a half, on a broad geographical scale, the empire writ large enjoyed both intensive and extensive growth. The Roman Empire both staved off Malthusian reckoning and earned uncalculated political capital.¹¹

This prosperity was the condition and the consequence of the empire’s grandeur. It was a charmed cycle. The stability of the empire was the enabling background of demographic and economic increase; people and prosperity were in turn the sinews of the empire’s power. Soldiers were plentiful. Tax rates were modest, but collections were abundant. The emperors were munificent. The grand bargain with the civic elites paid out for both sides. There seemed to be enough wealth everywhere. The Roman armies enjoyed tactical, strategic, and logistical advantages over enemies on every front. The Romans had achieved a kind of favorable equilibrium, if more fragile than they knew. Gibbon’s great History of the Decline and Fall of the Roman Empire launches from the sunny days of the second century. In his famous verdict, “If a man were called to fix the period in the history of the world, during which the condition of the human race was most happy and prosperous, he would, without hesitation, name that which elapsed from the death of Domitian [AD 96] to the accession of Commodus [AD 180].”¹²

The Romans had edged outward the very limits of what was possible in the organic conditions of a premodern society. It is no wonder that the fall of such a colossus, what Gibbon called “this awful revolution,” has been the object of perennial fascination.

OUR FICKLE PLANET

By AD 650, the Roman Empire was a shadow of its former self, reduced to a Byzantine rump state in Constantinople, Anatolia, and a few straggled possessions across the sea. Western Europe was bro...