What role did climate change and disease play in the fall of Rome?

Thomas Cole , " The Path of the Empire. Desolation "



Sooner or later, any Roman historian is asked where our society is now on the timeline describing the fall of Rome. Historians frown on such attempts to use the past, but even if history does not repeat itself, and does not fit beautifully into moral lessons, it can deepen our sense of what it means to be human and appreciate the real fragility of society.



In the middle of the second century, the Romans controlled a vast and geographically diverse part of the planet, from the north of Britain to the edges of the Sahara, from the Atlantic to Mesopotamia. In general, a prosperous community in peak reached 75 million. At some point, all free inhabitants of the empire were able to enjoy the rights of Roman citizenship. It is not surprising that the 18th century English historian Edward Gibbon called this era “the happiest” in the history of our species - however today we tend to see the advancement of Roman civilization as an unintended approximation of its death.



After five centuries, the Roman Empire turned into a small Byzantine stub-controlled state, controlled from Constantinople, yielding Middle Eastern provinces to Islamic raids, and western lands to German kingdoms. Trade faded, cities shrank, technological progress stalled. Despite the cultural vitality and spiritual heritage of past centuries, this period was marked by a decrease in population, political fragmentation and a decrease in the level of material complexity. When historian Ian Morris of Stanford University created a universal social development index, Rome’s fall manifested itself as the greatest reversal in the history of human civilization.



The explanation of the phenomenon of this magnitude is complete: in 1984, the German classicist Alexander Demandt compiled a catalog of more than 200 hypotheses. Most scholars considered the internal political dynamics of the imperial system or the changing geopolitical context of the empire, whose neighbors constantly improved their military and political technologies. But new evidence is beginning to reveal the critical role played by changes in the natural environment. The paradoxes of social development and the inherent unpredictability of nature worked together to bring the fall of Rome closer.



Climate change did not begin with exhaust pipes or industrialization, they were an integral feature of human existence. Orbital mechanics (variations in the tilt of the axis, the rotation and eccentricity of the Earth’s orbit) and the solar cycles change the amount and distribution of the energy received from the Sun. Volcanic eruptions spray sulphates with reflectivity in the atmosphere, which sometimes leads to far-reaching consequences. Modern anthropogenic climate change is so dangerous because it occurs quickly and together with many other irreversible changes in the Earth’s biosphere. But in itself, climate change is nothing new.



The current need to figure out the natural context of current climate change is just a gift for historians. Experts in the field of earth sciences are scanning its surface in search of paleoclimatic proxies, natural archives of the environment of the past. Attempts to bring climate change to the forefront of Roman history are supported by both new data and heightened sensitivity to the importance of the physical environment. It turns out that climate played a major role in the rise and fall of Roman civilization. The builders of the empire played into the hands of the right moment: the characteristic warm, humid and stable weather boosted the economic efficiency of the agrarian community. The benefits of economic growth supported political and social deals through which the Roman Empire controlled its vast territory. A successful climate, both implicitly and clearly, was the basis of the internal structure of the empire.



The end of a successful climate regime did not immediately, and in some simple way attracted the end of Rome. Just a less successful climate undermined its foundations precisely at the moment when empires were threatened by more dangerous enemies outside - the Germans, the Persians. Climate instability reached its peak in the 6th century, during the reign of Justinian I. Works by dendrochronologists and ice core specialists point to a monstrous spasm of volcanic activity in the 530s and 540s AD, which is incompatible with anything that happened a few thousand years before. This sequence of strongest eruptions triggered what is now called the " Late Antique Little Ice Age ", when a significant cooling was maintained for 150 years. This phase of climate deterioration has clearly affected the weakening of Rome. She was also closely associated with an even more terrible catastrophe: the first pandemic of the bubonic plague .



The breakdown of the biological environment further influenced the fate of Rome. With all the success of the empire, life expectancy fluctuated at around 25 years, and infectious diseases were the main cause of death. But the set of diseases that raged in Rome was not constant, and today's ideas and technologies radically change our understanding of evolutionary history - both of our species and of our microscopic enemies and allies.



The Roman Empire, with its high urbanization and interconnectedness, was a gift for its microscopic inhabitants. Such simple gastrointestinal diseases, such as shigellosis and paratyphoid, spread, infecting food and water, and flourished in densely populated cities. When draining wetlands and laying roads, malaria appeared in its worst form — the simplest parasites of Plasmodium falciparum carried by mosquitoes. The Romans connected the communities by sea and land, as they had never before in history, as a result of which microbes inadvertently spread on an unprecedented scale. Slow killers such as tuberculosis and leprosy entered their heyday in a network of interconnected cities, supported by the development of the Romans.



However, the decisive factor in Roman biological history was the arrival of new microbes capable of triggering pandemics. The empire was shaken by three intercontinental cases of disease. The Antoninov plague coincided with the end of the optimal climate regime, and probably became the global debut of the smallpox virus. The empire was restored, but could not regain its former influence. Then, in the middle of the third century, a mysterious affliction of unknown origin, Ciprian's plague , sowed panic in the empire. Although the empire was restored, it changed irreversibly - a new type emperor appeared in it, a new type of money, a new type of society and soon a new religion, Christianity. The most prominent episode was the pandemic of the bubonic plague that broke out in the sixth century during the reign of Justinian, a prelude to the medieval Black Death . The consequences are difficult to imagine - probably half of the human population died.



The Justinian Plague is an interesting case for the study of the extremely complex relationship between man and natural systems. The culprit of this event, the bacterium plague bacillus, the enemy is not particularly ancient; it appeared about 4,000 years ago, most likely in central Asia, and during the first pandemic was still newborn from the point of view of evolution. The disease is constantly present in the colonies of such social, living in the holes of rodents, like marmots or gerbils. However, the historical pandemics of the plague have become colossal accidents, bursts, including at least five different species: a bacterium, a rodent carrier that strengthens the host (a black rat living close to humans), a flea that spreads germs, and a person trapped between the hammer and the anvil.



Genetic evidence suggests that the strain of the plague wand that gave rise to Justinian's plague came from somewhere in the west of China. He first appeared on the southern shores of the Mediterranean, and most likely smuggled along the southern sea trade routes that carried silk and spices to Roman consumers. It was an accident of early globalization. When the microbe reached the rodent colonies that were raging with life, which were fattening on the giant grain stores in the empire, the increase in mortality could no longer be contained.



The pandemic of the plague has become a phenomenon of extraordinary environmental complexity. It took completely coincidental coincidences, especially if the initial outbreak that went beyond the rodent colony in central Asia was caused by the massive volcanic eruptions that occurred in previous years. It was also influenced by the unintended consequences of the man-made environment — the global trade routes that brought bacteria to the shores of Rome, and the prosperity of rats within the empire. This pandemic destroys all the differences between structure and chance, regularity and unforeseen circumstances. Here lies one of the lessons of Rome. People change nature - and above all, the environmental conditions in which evolution develops. But nature remains blind to our intentions, and other organisms and ecosystems do not obey our rules. Climate change and the evolution of diseases were elements of unpredictability in human history.



Our world today is very different from ancient Rome. We have a health care system, the theory of microbes and antibiotics. We will not be as helpless as the Romans are if we are wise enough to recognize the deadly threats hanging over us and use the tools we have to neutralize them. But the essence of the nature of the fall of Rome gives us a chance to rethink the influence of the physical and biological environment on changing the destinies of human communities. Perhaps we will consider the Romans not just as an ancient civilization, separated from us by an irresistibly long period of time, but as the creators of our present world. They built a civilization in which global networks, emerging infectious diseases and environmental instability became decisive forces in the fate of human communities. The Romans also believed that they would cope with the changeable and furious power of the natural environment. History warns us: they were wrong.



Kyle Harper is a professor of humanities and classicism, senior vice president and dean of Oklahoma University. His latest book is entitled: “The Fate of Rome: Climate, Diseases, and the End of the Empire” (2017).