Pathogenesis: A History of the World in Eight Plagues

by Jonathan Kennedy

The implication—that Roman imperialism imposed a superior culture on the warring, uneducated and dirty people of the Middle East—echoes the common claim that the British Empire brought civilization (in the form of railways, the English language, capitalism, etc.) to the societies it conquered, and is also apparent in justifications for more recent neo-colonial interventions, such as the invasions of Iraq and Afghanistan.

Even now, the water in the Trevi Fountain is supplied by an aqueduct dating from the first century CE.

There was an extensive network of drains under the imperial capital. This included the Cloaca Maxima, which was, according to Pliny the Elder, high and wide enough to allow the passage of a wagon loaded with hay. This drain was even protected by its own goddess, Cloacina.

Many homes had private toilets, which were often located in the kitchen.

Malaria had prevented attacks on the imperial capital since at least the late third century BCE,

But in his recent book The Fate of Rome, Kyle Harper gathers a large amount of evidence to show that a series of pandemics caused immense damage and played a crucial role in weakening the Roman Empire, not just in absolute terms but also relative to the neighboring “Barbarians.” This is because, although the term “Barbarian” is problematic in that it lumps together an incredibly diverse set of communities into one indistinguishable and supposedly inferior mass, all these groups tended to have one thing in common: they lived in much less-populated and less-connected societies than the Romans. As a result, pandemics tended to cause far more devastation to the Romans than to Barbarian societies. The differential impact of infectious diseases is a key factor in the political dynamics of the Roman Empire from the mid-second century CE until the fall of Constantinople to the Ottomans in 1453.

Even today, if patients are treated in modern medical facilities with the latest drugs, Ebola still kills half the people who contract it.

But the plague’s most lasting impact was not political. It was religious. The pandemic turned a tiny and obscure Jewish sect on the periphery of the empire into a major world religion, one that today has 2.3 billion adherents and accounts for almost a third of the world’s population.

It wasn’t a coincidence that the two high points of repression coincided with the Antonine and Cyprianic Plagues. Pagans believed that the presence of a new religion was displeasing the Roman gods or driving them away, and therefore Christianity was responsible for the widespread death and disruption.

How do we explain the sudden transformation of Christianity from a marginal Jewish sect to a popular religion? The American sociologist Rodney Stark argues that infectious diseases are a crucial part of the story. The Christian faith skyrocketed because it provided a more appealing and assuring guide to life and death than paganism during the devastating pandemics that struck the Roman Empire in the second and third centuries CE. In fact, he goes as far as to say that if it wasn’t for the Antonine and Cyprianic Plagues, “Christianity might never have become so dominant a faith.”

One major point of difference between the old and new faith was the issue of what happens when we die. Jesus promised everlasting life in paradise, whereas “pagans believed in an unattractive existence in the underworld.” Then there was the question of why pandemics occur: the Greco-Roman gods were capricious, angry, indifferent to human suffering and sometimes downright cruel.

Christianity provided another more tangible benefit over paganism. Traditional Roman society was not uncharitable—in its heyday, the state doled out free wheat and later bread to 200,000 people in the imperial capital, for example—but their deities did not reward altruism. So when plagues were raging, people of means—including Galen—took flight, and those who remained tried to avoid contact with the sick. Observing the pagans, Bishop Dionysius of Alexandria noted: “their dearest they fled from, or cast them half dead into the road.” Christianity was different. Believers were expected to show their love for God through acts of kindness to each other. As a result, followers of Jesus tried to guarantee entry into heaven with good deeds in their earthly lives. Dionysius describes how Christians looked after the ill during the Plague of Cyprian: “Heedless of danger, they took charge of the sick, attending to their every need.”

Christians would have been able to reduce mortality by up to two-thirds just with basic nursing, such as providing food and water.[48] The fact that so many more Christians survived, and that Christians managed to save pagans abandoned by their families, would have provided the best recruitment material any religion could ask for: miracles.

Although malaria didn’t stop Alaric from entering the great city, it did prevent him from basking in the glory of his achievement: the disease killed him soon afterward.[51] In the middle of the fifth century Attila the Hun rampaged across Roman territory. In 452 CE, his army razed Aquileia. The whole of the Italian Peninsula was defenseless, but after his army was struck down by a devastating disease—most likely malaria—Attila was forced to retreat to the high and dry Hungarian Steppe. It is not clear why the defensive shield that repelled invading armies for centuries finally cracked, but in 476 Romulus Augustulus was deposed by Odoacer, a soldier who led a federation of Germanic tribes and became King of Italy. This is traditionally seen as the end of the Western Roman Empire.

Just as in the old imperial capital, infectious diseases created a defensive force field around the new one. In 447, an earthquake destroyed Constantinople’s defenses and left it exposed. The Huns closed in on the city but were sent packing by gastrointestinal bugs. According to one chronicler, “He who was skillful in shooting with the bow, sickness of the bowels overthrew him—the riders of the steed slumbered and slept and the cruel army was silenced.”

From plague bacteria’s perspective, humans and black rats are second-rate hosts because of their tendency to die quickly after the pathogen enters their bodies. Some other species, most notably great gerbils and marmots, both of which live in mountainous areas of Central Asia, have partial resistance to Yersinia pestis. Their bodies provide an environment where the bacteria can reproduce without killing the host. This means that while plague epidemics quickly burned out in human and rat populations, the pathogens could survive for centuries or even millennia in gerbils and marmots, before once again spilling out into the rat and then human populations when conditions allowed.

He claims that 10,000 people died every day in Constantinople at its height. This might well have been an exaggeration, but the message is clear: the outbreak was devastating.

In the south and west of the Arabian Peninsula many inhabitants—including Muhammad—lived in permanent settlements. But a large proportion of the population were nomadic Bedouins. On the origins of the word “Arab,” Mackintosh Smith points out that “for more of known history than not, the word has tended to mean tribal groups who live beyond the reach of settled society…it is certainly what they were during most of the second AD millennium.”[70] Consequently, the region was much less prone to a disease that was spread by flea-carrying rats, and the Roman and Persian Empires were weakened not only in absolute terms but also relative to the newly Muslim and united Arabs.

But the Arab commanders learned that when an epidemic struck it was safest to remove their troops from the city to isolated highland or desert locations until the danger had passed. Similarly, the Umayyad Caliphs would retreat to the desert palaces and live like Bedouins during plague season.

Without the lethal effects of Yersinia pestis, it is almost impossible to imagine that Islam would have blossomed from a sect with a small group of followers in the Hijaz to a major religion practiced by almost a quarter of the world’s population, or that Arabic would have gone from being the language of a few desert tribes to one that is now spoken by almost half a billion people across North Africa and the Middle East.

How do we account for the decline of medieval Europe and the emergence of the modern world? The Black Death played a crucial role, triggering a series of events that—over several centuries—resulted in this transformation. It was, as one historian put it, “the great watershed in medieval history” that ensured “the Middle Ages would be the middle, not the final, phase in western development.”[3]

Supposedly, Italian merchants contracted plague in the autumn of 1346 when Mongol soldiers besieged Kaffa and catapulted the corpses of plague victims over the city walls. This story is apocryphal, but that hasn’t stopped some scholars identifying it as the first instance of biological warfare.

Another eyewitness in Florence wrote of throwing bodies into a mass grave, covering them with earth, adding more bodies and then earth, “as one makes lasagne with layers of pasta and cheese.”

The Norwegian historian Ole Benedictow estimates that roughly 60 percent of the population of Europe—that is about 50 million out of 80 million people—died from the plague between 1346 and 1353.

“it is a curious and somewhat humiliating reflection on human nature that the European, overwhelmed by what was probably the greatest natural calamity ever to strike his [sic] continent, reacted by seeking to rival the cruelty of nature in the hideousness of his own man-made atrocities.”

The demographic scar left by wave after wave of plague was deep and abiding. The population did not return to its 1300 level until the sixteenth century in Italy and France, the eighteenth century in England, and the nineteenth century in Egypt, which was at the time part of the Ottoman Empire.

The introduction of regulations such as quarantine and cordons sanitaires in late-medieval societies had significance well beyond public health, because they extended state power into areas of human life that had not previously been subject to political authority. Michel Foucault saw the shift in the focus of states from controlling territory to governing people’s bodies as a key feature of the modern world.

What is more, according to Mikhail the colonization of the Americas was a response to the realization that the Holy Land was irretrievably lost.

Christianity had once replaced paganism because it provided a more appealing and assuring guide to life and death during the Antonine and Cyprianic Plagues. Now, as disease ravaged the population yet again, many people began to reject the teachings of the Catholic Church.

By the mid-fourteenth century, the Catholic Church had drifted a long way from the message of humility, compassion and faith preached by Jesus and his followers. This time round there was no upstart religion to offer an alternative to Christianity, as it had once done to paganism. Instead, the insurgency came from within the established faith.

In this sense, existential questioning triggered by the Black Death didn’t just lead to the rise of Protestantism but also paved the way for the emergence of secularism.

He argues that what he calls the Protestant ethic has an “elective affinity” with the spirit of capitalism.

For over 1,000 years, fervent Catholics had locked themselves away in monasteries. Devout Protestants instead applied this ascetic ideal to their everyday life, working hard and investing their savings; and this change in focus was responsible for the transition from the feudal system to capitalism.

It was only in England that the post–Black Death conflict between the lords and peasants resulted in the demise of feudalism and the transition to capitalism.

In 1363 Parliament issued a Sumptuary Law that decreed the types of clothes people at different levels of society could wear, and even what they were allowed to eat. These rules were unenforceable—even the majority of pilgrims in The Canterbury Tales wore swankier clothes than were permitted—but the fact that such laws were thought necessary indicates that the lords felt threatened by the conspicuous consumption of the newly affluent commoners.

The competition between these remaining tenant farmers resulted in a new pattern of dynamic and sustained growth in output that amounted to nothing less than a Second Agricultural Revolution.

“Wherever the European has trod, death seems to pursue the aboriginal.”

Eyewitness accounts describe Spaniards drowning in the water, weighed down by looted treasure that they had melted into gold bars. This tale might sound a bit too much like a Herzogian allegory for the crazed greed of the conquistadors, but in 1981 a 2-kilogram ingot was dug up during building work in downtown Mexico City along the Spaniards’ escape route and tests have shown that it was forged in 1519 or 1520.

The scale of the cumulative devastation is hard to imagine: the indigenous population of Mesoamerica was about 20 million when Cortés arrived but had fallen to 1.5 million a century later.

Smallpox is, as Alfred Crosby puts it, “a disease with seven-league boots.”

Across the whole of the Americas, the introduction of infectious diseases from Europe resulted in a 90 percent fall in the population, from about 60.5 million in 1500 to 6 million a century later. The global population fell by 10 percent. The decline in slash-and-burn agriculture and the reforestation of tens of millions of hectares of cultivated land resulted in a reduction in carbon dioxide in the atmosphere that is visible in the ice cores drilled by scientists in the Antarctic. The demographic collapse cooled the global surface air temperature by 0.15 degrees Celsius, contributing to the Little Ice Age in the early 1600s.

And yet there is evidence of only one infectious disease being transmitted from Native Americans to Europeans: syphilis.

How do we explain the almost unilateral flow of pathogens from Europe to the Americas, despite relatively high population densities in Mexico and Peru? The infectious diseases that evolved to infect humans in the wake of the Neolithic Revolution originated in domesticated herd animals.

Unlike the ancestors of Eurasian farm animals, alpacas and llamas hadn’t lived in vast herds prior to domestication, limiting the opportunities for diseases to emerge and become endemic.[32] As a result, the Neolithic Revolution in the Americas doesn’t appear to have been accompanied by a devastating epidemiological revolution.

The fact that diseases caused by Old World pathogens almost exclusively killed Native Americans was interpreted on both sides as an unequivocal sign that God or the gods supported the Spanish invaders. It added to the conquistadors’ belief in the righteousness of their gory, greedy mission.

The Native Americans were ripe for conversion to what, based on the evidence they had available to them, appeared to be a far superior religion. They embraced Catholicism with a fervor that is still very much apparent: today, 40 percent of the world’s Catholics live in Latin America.

The Cerro Rico at Potosí is located in the Andes in what is now southern Bolivia at an altitude of 4,000 meters, a two-and-a-half-month journey via pack animal from Lima. It contained so much high-grade silver ore that it provided about 80 percent of the silver mined across the world over the next 250 years.

Revenue from Potosí made Spain enormously rich for a while, but the newfound prosperity didn’t kick-start a process of self-sustaining economic growth. Rather, feudal Spain used the almost unfathomably large proceeds of Latin American colonialism to fund a series of costly and lengthy wars.

In the Philippines, European merchants exchanged South American silver for spices, silk and porcelain to be sold back home. This marked the beginning of a genuinely global economy in which the Old World was intricately connected to the New World.

The Spanish succeeded in colonizing the Americas because they were aided by bacteria and viruses. The Norse were not and failed. In fact, because of their own isolated existence, the European inhabitants of Greenland and Iceland were almost as vulnerable to Old World pathogens as the indigenous people of the New World.