Both Thucydides and Clausewitz give great emphasis to the role of chance or luck plays in the course of military events. The former, however, uses chance in a far wider sense, as much more than just the impact of luck on a particular battle or the appearance of some factor that represents an immediate surprise to those concerned. The Greek word Thucydides uses to describe chance is tyche. Interestingly translators more often than not fail to translate tyche, but simply leave it out as being of no importance. In fact, it is of enormous importance, because tyche interferes with human affairs from the lowest to the highest levels. In 431 BC, the Thebans launched a surprise attack on their smaller neighbor Platea. It should have worked. A small commando force crossed the mountain between the two cities and gained entrance into the city at dusk. The Plateans panicked and the Thebans seized control of the city. A large force was supposed to follow in its wake, but in the night an unexpected heavy spring downpour occurred; the rain extinguished the torches; the guides lost their way; and the army floundered its way to Platea only to arrive so late that the Plateans had shut the gates and captured the commando force. The unexpected, chance or tyche, robbed the Thebans of their expected victory.
We might, thus, define tyche in some case as happenings beyond the control of human beings—and in this regard, we now have a historical record that suggests the immense impact chance happenings, driven by natural factors, have had on the course of history. They also provide a dark warning for the future. In The Fate of Rome:, Climate, Disease & the End of an Empire, Kyle Harper has presented us with a case study, namely the collapse of the Roman world in the period between the third and sixth centuries CE. Here tyche, in the largest sense, created a perfect storm of disastrous natural events and happenings that brought about the complete collapse of the Western Roman Empire in the fifth century CE, and eventually the ability of the Eastern Roman Empire to control much of the Mediterranean world after the seventh century. These natural events created conditions the Roman world was incapable of understanding, but which nevertheless brought about the collapse of one of the greatest, longest lasting empires in history. What Professor Harper’s book underlines is that the military difficulties that Rome’s generals and soldiers experienced in the period from the third century on were only the surface manifestations of far deeper systemic changes that could not be predicted, but which in combination created a perfect storm. Thus, fate, or more accurately tyche, undermined the best efforts to prevent what turned out to be a disastrous collapse.
The slide to catastrophe began after a period of unparalleled prosperity that had seen the population of Rome grow from approximately 60 million under Emperor Augustus in 33 BC to 75 million in 165 AD. The historian Edward Gibbon would describe the period in the following terms: “If a man were called to fix a 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 period. Significantly, archeological and scientific evidence indicates the period from 200 BCE through the mid-point of the second century CE was extraordinarily favorable in terms of its climate for agriculture and the development of an extensive and expansive civilization in the Mediterranean and Western Europe. Combined with the favorable weather was a period of general peace under the empire that, for the most part, removed the generally disastrous role played by war throughout history. Except for one short period of civil wars between the claimants to Nero’s throne (70-71 CE, the year of the three emperors) and the two Jewish rebellions (66-71 CE and 135 CE), Rome fought its wars on the frontiers: the Rhine, the Danube, and Syria.
All that changed in the midst of the rule of the emperor Marcus Aurelius. The traditional narrative suggests that in 165 CE Roman soldiers returning from the campaign against the Parthians in Mesopotamia brought a plague. In fact, the pathogen most probably came through the Red Sea, brought by traders. In the great urban centers of the empire, all closely linked, it found an ideal environment. Given the extent of trade among these urban centers, the smallpox pathogens spread rapidly from urban center to urban center. As Professor Harper points out, “[i]n one sense, the Antonine Plague was a creature of chance, the final unpredictable outcome of countless millennia of evolutionary experimentation. At the same time, the empire—its global connections and fast-moving networks of communications—had created the ecological conditions for the outbreak of history’s first pandemic.” We have no way of knowing how many died, but it was substantial, on the order most probably of what was to occur in the Black Death of the fourteenth century.
Had the Antonine Plague been the only major problem besetting the Romans, the empire would likely have weathered the initial storm without catastrophic results. It was, however, not the only major factor that would affect the long-term health of the empire, based as it was on the slight surpluses that subsistence agriculture produced. Almost concurrently with the Antonine Plague, the weather patterns across the Mediterranean and Europe, reaching into central Asia, began a slow, steady shift that resulted in an average drop in temperature and rainfall. That decline would continue through to the mid-fifth century, which was to see the beginning of an even colder period, what climatologists are now calling the “Late Antique Little Ice Age”—one that was even less favorable to agriculture.
The combination of these two natural phenomena, plague and climate change, led to the crisis of the third century, which was to see civil wars of an extent not seen since the collapse of the Roman Republic, disasters on the frontiers, massive barbarian invasions by the Goths that reached even into Italy and Syria, Roman defeats that came close to destroying the empire, and a complete collapse of the currency. Moreover, global climate change led to the movement of the barbarian tribes beginning in Central Asia, which, like a set of dominoes, tumbled toward an empire with little of the resiliency that marked the strength of the state one hundred years earlier. The empire did not collapse in the fourth century, as a group of warrior emperors put it back together. However, the final collapse in the west came at the end of the fifth century with another wave of barbarian invasions, which drove the Goths again to seek shelter in the empire. Gross incompetence, political as well as military, then led to the disastrous defeat of Roman armies at the hands of the Goths at Adrianople in 378 CE. The arrival of the Huns helped to finish off the western empire, while the sack of Rome in 410 CE signaled the end of the empire in the west.
The Eastern Roman Empire, however, held together, and by the early sixth century it seemed in a position to regain control of the whole Mediterranean basin. Under the Emperor Justinian and his brilliant general Belisarius, Constantinople, the new Rome, regained control of much of North Africa, Sicily, and Italy. Again, nature intervened. The unexpected appearance of tyche hit the Eastern Roman Empire with three terrible blows. The last blow was expected, given the historical record, but the extent of the damage done was unexpected: the war between the empire and Persia, which exhausted both empires to the point of collapse. But the other two blows, no seer could have predicted. The first was the third great plague to hit the empire within the space of four centuries. For the first time in history, the bubonic plague appeared in the Mediterranean, and the swath of death it inflicted on the empire’s population appears to have been on the order of what it was to inflict on Europe’s population in the fourteenth century.
For the short term, there were also massive volcanic explosions that blotted out much of the sun’s energy, the first in 536 CE AD with and a second in 539-540 CEAD. The locations of these eruptions is unknown, but the evidence in ice caps is overwhelming. The impact was devastating.. The volcanic blasts, reminiscent of the explosion of Mount Tambora in 1815 that resulted in what was called the year without summer in the northern hemisphere, had a direct impact on the world’s temperature equilibrium. The drop in Europe’s summer temperature was on the order of 2.5 degrees centigrade. Moreover, the decade from 536 to 545 appears to have been the coldest over the past two millennia. The evidence from the literary sources fully supports the scientific evidence. One commentator of the period noted, “We have had a winter without storms, a spring without mildness, a summer without heat.”
But in the longer term, at almost the same time the great volcanic explosions occurred, the sun stopped producing energy at its earlier levels. “A grand solar minimum, centered on the late seventh century, was the greatest plunge in energy received from the sun during the last 2,000 years. It was lower even than the Maunder minimum of the seventeenth century.” The combination of these short-term and the long-term events altered weather patterns across the empire, and not necessarily for the benefit of those living there.
The third blow to the empire, which was to be expected, given human nature, was a great war between the Persians and the Eastern Romans. By 626 CE, the Persians were at the gates of Constantinople; two years later the Byzantines had driven them out of Anatolia and Syria. But to the triumph was short lived. Exhausted by plague, declining agricultural production, and the vicious impact of the bubonic plague, the Eastern Roman Empire was defeated by the Arab armies exploding from the deserts of Arabia in the single battle of Yarmouk in 636 CE only eight years after regaining Jerusalem from the Persians. The empire simply no longer had the strength to regain Syria, Egypt, and North Africa. In effect, the Byzantines would shrivel up into an area that was to consist of Anatolia and small pieces of Greece and the Balkans. Equally important was the fact that the Mediterranean was now to find itself divided between the Christian states to the north and Muslim states to the south. In the long term, the Western Europeans would turn away from the Mediterranean and begin the process of creating their own disputatious societies in the backwaters of what had been a part of the great Roman Empire in the west and its areas beyond the Rhine and Danube controlled by the barbarians.
So what are we to make of these great natural events that so distorted and then destroyed one of the most successful empires in history? We could, of course, ignore the past as having little relevance to thinking about the future. On the other hand, for those willing to grapple with the uncomfortable, the past would suggest that governments and their military organizations need to develop the capacity to adapt not just to the terrible problems that modern war brings in its train, but to the kinds of chance that the natural world might spring on them. It is not that they need to prepare for a specific future. Rather, they need to develop the kind of thinking that can adapt to the frightening surprises that will inevitably occur in the future, such as a volcanic explosion on the order of the eruption at Mount Tambora in 1815, one that might reduce the world’s food production by 30 percent. Moreover, the very nature of a globalized world, with a population reaching toward the level of 8 billion, interconnected by swift transportation, and with some its great cities still beset with raw, untreated sewage, would seem the ideal setting for a pandemic beyond our comprehension.
Professor Harper has produced a wonderful case study that demands a general rethinking of how we view the decline and fall of the Roman Empire. It turns much of the earlier views on Rome’s decline into surface explanations and places the chance happenings of nature in a driver’s seat that we can barely comprehend. It should also give us pause in how we think about the future. Tyche in the most terrible sense of the Greek word is out there waiting for us.
Williamson Murray is Professor Emeritus of History at Ohio State University.
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Header Image: "Destruction" from The Course of Empire by Thomas Cole (Wikimedia)
 Personal discussion with Donald Kagan, 2010. For more on tyche, see Williamson Murray, "Thucydides: Theorist of War," Naval War College Review 66, no. 4 (Autumn 2013), http://digital-commons.usnwc.edu/nwc-review/vol66/iss4/5.
 The Fate of Rome, Climate, Disease & the End of an Empire. Kyle Harper. Princeton: Princeton University Press, 2017. p. 64.
 Ibid. p. 252.
 Ibid. p. 254.