4. Water, sewers, and empires
Introduction: the importance of biology
It is a major contention of this book that infectious disease has greatly influenced historical events. In this chapter, we consider the effect of disease, especially waterborne infections, on three major civilizations: the ancient Egyptians, the Indus Valley civilization, and the Roman Empire. Orthodox history emphasizes the actions of leaders, the strategies of generals, the policies of governments, and so forth. Sometimes the subsurface layer of economics is put forward as an underlying cause. But economics depends on the availability of raw materials and natural resources. However competent your rulers are and enlightened your fiscal policy is, creating a thriving society in a desert is difficult—unless, of course, you strike oil! This brings us to the realm of biology. Oil and coal are largely biological in origin: the decayed remains of vegetation that died many millions of years before man walked on Earth.
Behind politics lies economics, and behind economics lies biology. So then, I argue, to fully understand both history and current events, we need to include the biological perspective. Although this book focuses on the effects of disease, other biological effects are also important—these include environmental degradation, climate change, overpopulation, and pollution. In addition, these factors can help promote the spread of disease.
Irrigation helps agriculture but spreads germs
The first cities grew up alongside rivers: the Tigris and Euphrates, the Nile, and the Yellow River. Irrigation led to increased crop yields, which led to higher population density. These ancient river-based cultures then came to dominate the surrounding areas.
Ancient Egypt is remarkable for the long periods its regimes survived. The imperial Chinese dynasties that originated in the valley of the Yellow River were similarly long-lived. Settled agricultural societies based on irrigation are noted historically both for long-term stability and for the subservience of their common people. Irrigation requires large-scale public works, which, in turn, requires organized mass labor, which requires an autocratic state to control the lower classes. This political explanation ignores the fact that needs are not fulfilled by magic. Infection supplies the missing mechanism. Irrigation is extremely effective in spreading infections among agricultural workers. Waterborne diseases included a wide range of bacteria, viruses, and parasitic worms.
The class system, water, and infection
Throughout history, human societies have tended to divide into classes or castes of varying rigidity. Even in the same nation, even if they share the same religion and speak the same language, individuals of higher status avoid mixing with those of lower status. Early societies, primitive tribes, and social apes such as baboons all have a hierarchy, although they lack rigid divisions. Class systems are not based on merely social forces. Although those forces might contribute to class segregation, deeper biological reasons exist.
Infectious disease has always hit the poor and lowly far worse than the prosperous and powerful. Avoiding members of lower and more disease-ridden groups was not merely a matter of status. In the eighteenth and nineteenth centuries, for an upper-class Englishman to associate too closely with the working classes would have doubled his risk of tuberculosis. Respectable people did not associate with their social inferiors or visit houses of ill repute. Both sexual and social respectability reinforce avoiding infection. Today the threat of infectious disease has greatly diminished in the industrial nations. And yes, now that it’s safe, every political leader who wants to pick up some cheap popularity arranges to “mix with the people.”
Infection might also help keep the lower orders in their proper place. Even nowadays, some 50% of the Egyptian population is infected with assorted parasitic worms. Their feeble performance in the Arab–Israeli wars has been attributed in part to the debilitation of Egyptian soldiers by disease. In ancient Egypt, the peasants who waded barefoot in the flooded fields would almost all have been infected by parasitic worms carried by water snails (schistosomiasis). The military aristocracy would have been far healthier, stronger, and more vigorous. In contrast, unsettled peoples, such as the Huns, Mongols, Vandals, and Arabs, tend to be difficult to rule and their empires short-lived. Here, the lower classes are not subject to debilitating disease as an inevitable result of their economic role.
The origin of diarrheal diseases
The human gut provides a home for colossal numbers of bacteria. In the small intestine, mixed in with the material being digested are several million bacteria per gram (1 oz = 28.4 g). In the large intestine, the numbers per gram can rise to 100,000 million, or more than 20 times the world’s human population. The vast majority of these bacteria are harmless, and some are beneficial by aiding digestion, making vitamins, or defending their habitats against other, more dangerous intruding microorganisms.
As we have already seen, from time to time, one of our harmless microbial inhabitants goes bad and causes disease. In addition, harmful newcomers might originate from other animals. Most of these newcomers probably arrived only after denser city populations provided more opportunities. In primeval times, outbreaks of a novel infection would have been confined to one or a few bands of nomadic hunters, and the disease would not have survived for long. As human populations got denser, they provided more scope for rogue microorganisms to circulate further and live longer.
Viruses that live in the intestine follow much the same pattern. These viruses infect the cells of the gut lining and cause a small amount of damage. Most cause so little damage that they go virtually unnoticed. A few trigger outbreaks of diarrhea. Rotavirus is the most common virus that causes infant diarrhea. In third-world nations, it can be life-threatening, although in industrial nations it is rarely dangerous. Rotavirus has been with mankind long enough for special adaptations to evolve. The protein, lactadherin, is synthesized in the breast and found in human milk. Instead of being digested by babies, it remains in their intestines. Lactadherin mimics the receptor on intestinal cells to which rotavirus binds. When rotavirus binds to lactadherin, instead of attaching to the intestine, the virus remains floating in the gut and is flushed out. Infants whose mothers provide them with higher levels of lactadherin suffer much less from rotavirus-induced diarrhea.
Cholera comes from the Indian subcontinent
We can only speculate on the effects of infectious disease on the earliest civilizations. However, intestinal diseases were probably the first to topple whole human cultures. The first civilization whose collapse can be reasonably credited to infection is the Indus Valley culture, sited in what is now Pakistan and part of northern India. Good evidence indicates that cholera or a closely related waterborne infection might have been instrumental in its collapse. To understand this, we first need to consider the natural history of cholera itself.
Cholera is caused by the bacterium Vibrio cholerae. Its victims suffer severe diarrhea and can die of dehydration if not cared for. Cholera is thought to have origins in India and emerged onto the world stage only in the nineteenth century. Hindu physicians first described cholera around 400 B.C., but the disease was almost certainly endemic there much earlier. It has caused epidemics in India ever since, especially in the region of the Ganges delta. Hindus from all over India make pilgrimages to Benares, a holy city on the Ganges. Pilgrims in large numbers moving to and fro across India tend to spread waterborne disease between major population centers. This adds to the effect of the dense local populations in contaminating the Ganges River complex and the Bay of Bengal into which it empties.
Cholera stayed in India until the early 1800s. During the following century, half a dozen worldwide pandemics erupted. In 1817, cholera spread both westward to the Middle East and Southern Russia and eastward to Malaya, Thailand, and Japan. It reached England in 1831 and North America the next year. Another cholera pandemic was responsible for massive casualties during the Crimean War of 1854–1856. Of 250,000 troops engaged, the British and their allies lost approximately 20,000 to cholera.
But why did cholera not sweep through the unhygienic cities of Europe and Asia until the 1800s? European ships were in regular contact with India from the 1500s, and British troops and traders in India suffered substantial losses from cholera while in India. The answer is unknown, but a reasonably convincing suggestion is that cholera outbreaks burn themselves out in a few weeks, unless they can infect fresh victims. The slow-sailing ships of earlier times took a relatively long time to reach Europe, so cholera taken aboard in India could not survive the voyage. Faster steamships and the opening of the Suez Canal have since brought East and West into much speedier contact.
Cholera and the water supply
In 1832, John Snow investigated the cholera outbreak at Killingworth colliery near Newcastle in northern England. He concluded that cholera was not carried by bad air or passed directly from person to person. He blamed the constant diarrhea, unwashed hands, and shared food. The miners stayed in the pit for eight or nine hours, taking their food and drink with them. As one informant put it:
I fear that our colliers are no better than others as regards cleanliness. The pit is one huge privy, and of course the men always take their victuals with unwashed hands.
Snow continued his detective work in the London slums. The poor, crowded together in dirty conditions, were easy targets for cholera. But how did the rich contract the disease? Snow realized that the communal water supply could be contaminated by infected sewage. This explained why some communities were hard hit, whereas others, close by but supplied by a different water main or drawing water from a different well, remained unscathed. In the cholera epidemic of 1851, there were 4,093 deaths among the 266,000 people who drank water supplied by the Southark and Vauxhall water company that got water from the sewage-laden River Thames. In contrast, there were only 461 deaths among the 173,000 people whose water was supplied by the Lambeth water company, whose sources were uncontaminated.
Snow demonstrated that cholera is spread by contamination of water with the copious diarrhea its victims generated. England, followed by the other industrial nations, then took action to keep its water supplies clean. By the beginning of the twentieth century, most European and North American cities were as clean as the Romans had been in the first century. That’s progress! The last great cholera pandemic, which began in India in 1891, reached only as far as Russia. Western Europe went essentially unscathed.
The rise and fall of the Indus Valley civilization
The Indus Valley civilization flourished from about 3,000 B.C. to 2,000 B.C. and was centered around the Indus and Sarasvati Rivers in what is now part of northern India and Pakistan. By virtue of its location, the Indus Valley civilization was able to spread over a much larger area than the ancient civilizations of Egypt and the Middle East. Its two best-known cities were Harappa and Mohenjo-Daro, both now in southern Pakistan. Estimates of the population of Mohenjo-Daro range from around 30,000 to as high as 100,000. More relevant to infectious disease, several dozen towns of various sizes sprawled over the region, resulting in a large overall population, all in reasonable contact.
The Indus Valley towns were notable for being laid out in a well-designed grid. Streets were of fixed widths, 9m for main roads and 3m or 1.5m for lesser streets. Most houses were built to standardized designs with bricks of fixed sizes; the relative dimensions of virtually every brick used in the Indus Valley culture were 1 × 2 × 4. Perhaps the major achievement of the Indus Valley culture was its water supply and drainage system. All major centers had sophisticated communal plumbing, with water supply channels and drains. Almost every house in major centers such as Mohenjo-Daro had its own baths. Drains took the dirty water to a communal underground sewage system. The Great Bath of Mohenjo-Daro was the earliest public bath in the world. It measures 12m × 7m × 2.4m deep (approximately 40 ft. × 23 ft. × 8 ft.). Although no one really knows, most archeologists think that it served for religious purification, that it was a sort of baptism tank instead of a swimming pool. In any case, it was built of tightly fitting bricks that were plastered over and lined with a layer of bitumen, to make it waterproof.
Despite these initial technological advances, the Indus Valley culture remained stagnant, showing little progress beyond its initial achievements. Eventually, it collapsed, leaving no obvious successor culture. Around 1900 B.C., the Sarasvati River dried up, and its ancient course was rediscovered using satellite photos only in the 1990s. In contrast, several other minor rivers changed their courses to empty into the Indus River, which became overswollen and inundated its flood plain. By 1800 B.C., the Indus Valley culture had disappeared virtually without a trace, and urban civilization did not return to India for a millennium.
Were the changes in the rivers responsible? Some archeologists believe so. All the same, the cultures of Mesopotamia had to contend with floods, droughts, and the movement of the channels of the Tigris and Euphrates rivers. Although individual cities and regimes fell casualty, the culture as a whole did not collapse; the people relocated to other sites and continued evolving. The collapse of the Indus Valley culture has also been attributed to the arrival of the Indo-European (Aryan) invaders from the north. However, despite the usual exaggerated claims of antiquity typical for sacred writings, the Rig Veda, telling of the Aryan incursions, was assembled no earlier than 1,000 B.C. and was not written down for another thousand years. Thus, the invaders arrived long after Harappa and Mohenjo-Daro were already abandoned mounds. Furthermore, life in the countryside appears to have carried on with relatively little discontinuity during the collapse of the Indus Valley cities. Some archeologists talk of a “systems collapse,” which means that they have no idea why it collapsed but find it embarrassing to admit this in front of laypeople.
Cities are vulnerable to waterborne diseases
After a millennium of highly organized urban life, cities scattered over hundreds of miles were all abandoned within a century or two. To explain the collapse of an entire civilization on such a scale, we need a reason why urban life became nonviable, yet rural life went on. The latest archeological levels of Harappa and Mohenjo-Daro revealed large numbers of unburied skeletons. Although this originally suggested invasion and conquest, closer examination of the skeletons has shown that they lack the characteristic marks typically left by swords, axes, and other weapons. This implies that the slaughter was not due to human agency. The only realistic alternative is an epidemic of some kind. The great strength of the Indus Valley civilization was also its Achilles’ heel (despite the fact that Achilles would not be born for another 500 years!). A water-distribution system can also distribute waterborne disease. This is well illustrated by the 550 outbreaks of waterborne disease documented in the United States between 1946 and 1977. Although few were serious, these numbers illustrate the constant vigilance necessary to ensure a safe water supply.
City-dwellers in Harappa and Mohenjo-Daro got water from public wells whose rims were usually within a few inches of the ground. The drainage system was underground, though buried only a foot or two below the surface. Whenever drains backed up due to blockages or local flooding, there would have been massive contamination of the water supply. In fact, the system is so susceptible to contamination that early archeologists did not believe that the drains could have been used for human excrement. However, later excavations revealed latrines connected directly to the drainage system and the presence of wooden mesh baffles for screening out solid waste. Refuse heaps left by maintenance workers who entered the drains by manholes in the streets demonstrate that blockages were not uncommon.
Today we might wonder how they got away with this for a thousand years. The answer seems to be that highly virulent waterborne diseases had not yet evolved when the Indus Valley cities were first built. As we have already discussed, most virulent epidemic infections have emerged only in the last few thousand years. Before dense populations that shared the same water supply and sewers arose, severe diarrheal diseases had no way to spread. During the period from 3,000 B.C. to 2,000 B.C., bacteria that had previously relied on occasional mild diarrhea to wander from intestine to intestine were presented with ideal conditions for evolving into virulent waterborne killers. To put it rather unkindly, the evolution of cholera could well be the legacy of the Indus Valley culture. Cholera is perhaps the most likely agent, especially because it was known in India from early times. But because more than a thousand years passed between the fall of the Indus Valley culture and the earliest convincing descriptions of cholera, other diarrheal diseases, caused by related enteric bacteria such as Shigella or Salmonella, might have been the cause.
When a virulent form of cholera had evolved, it would have rapidly spread from city to city throughout the Indus Valley region. The older and larger cities would have been most susceptible, whereas rural communities would have suffered far less. Before modern medicine, epidemics of cholera typically killed a high proportion of those infected within a few days. When an epidemic struck, many city-dwellers fled to the countryside, probably under the impression that they had offended the gods. If you doubt that disease could cause the abandonment of entire cities, remember that, in medieval Europe, the death rate in the cities was greater than the birth rate, and the city populations were maintained only by continued immigration from the countryside.
Why didn’t waterborne disease wipe out other urban cultures? Consider the Romans, who had an extensive system for water distribution. For one thing, the Roman sewer system was more effective in removing human waste. The Romans might have turned the River Tiber into a giant sewer, but the Romans did not generally use it for drinking water. Instead, aqueducts brought water supplies a considerable distance from elevated and sparsely populated regions. The aqueducts kept the water high off the ground, away from possible contamination. If anything, diseases that rely on contaminated water were kept at bay during the Roman period. Before moving on to consider what kind of diseases were the undoing of the world’s greatest empire, let’s reflect that the fall of Rome, and the collapse of its civil engineering system, provided the opportunity for diarrheal diseases to make a major comeback.
Cholera, typhoid, and cystic fibrosis
An interesting recent revelation is that cystic fibrosis is linked to cholera resistance. Cystic fibrosis is an inherited disease that affects about 1 in 2,000 white children but is rare in other races. You must inherit two defective copies of the gene, one from each parent, to suffer from the disease. Humans who have a single defective gene are carriers but do not show symptoms, because a single good copy of the gene is sufficient for normal health. The molecular basis of cystic fibrosis is a failure to secrete chloride ions across cell membranes. Water normally flows to follow the chloride ions. Deficient water flow means that the mucus that lines and protects the lungs is abnormally thick due to a lack of sufficient water diluting it. This not only obstructs the airways but also allows the growth of harmful bacteria. The bacteria are protected from the immune system by the mucus, which they also use as a source of nutrition. Cells lining the airways of the lungs are killed and replaced with fibrous scar tissue, hence the name of the disease. Eventually, the patient succumbs to respiratory failure.
In cholera, death results from dehydration. The mechanism involves the initial release of ions, including chloride, from intestinal cells. Water follows the ions, and diarrhea results. If one defective copy of the cystic fibrosis gene is present, chloride ions and water move more slowly, and this protects against water loss via diarrhea. Consequently, a single defective gene protects against cholera—or, for that matter, any other disease that causes diarrhea and dehydration—but does not inhibit water flow enough to cause cystic fibrosis.
About 4.3% of the white population carry one defective copy of the cystic fibrosis gene, and 0.05% have two defective copies. Until very recently, nobody who received two bad copies and, therefore, suffered from cystic fibrosis lived long enough to have children. This allows us to calculate the rate at which bad copies of the gene are eliminated from the gene pool. For the incidence of cystic fibrosis to stay constant, defective copies of the gene must be created by mutation at the same rate at which they are lost by selection. In practice, the required mutation rate turns out to be a hundred times higher than naturally occurring mutation rates. This tells us that the prevalence of cystic fibrosis cannot be due to the constant emergence of new mutations. On the contrary, the cystic fibrosis mutation, when present as a single copy, is somehow being favored and preferentially passed on. Deeper genetic analysis also shows linkage disequilibrium. This means that mutant versions of the cystic fibrosis gene are associated with particular versions of neighboring genes much more often than expected by chance. This confirms that the mutant version of the cystic fibrosis gene is being passed on in association with these nearby genes instead of being constantly re-created by new mutations appearing at random.
Many slightly different mutations at different sites within the cystic fibrosis gene can produce defects, and around 50 different defective versions of this gene have been detected. Nonetheless, 90% of defective cystic fibrosis genes found in Northern Europe have the same defect at the molecular level (the amino acid phenylalanine at position number 508 is missing). The other 10% include some 40 different defects. This indicates that the majority of defective genes have been inherited from a relatively small group of ancestors instead of appearing by random mutation. For the defective version of the cystic fibrosis gene to be maintained at its present level by inheritance, those who have a single bad copy can be calculated to have a preferential survival rate of 2.3% over those with two good copies.
But is this preferential survival really due to cholera resistance? If true, we would expect cystic fibrosis to be most common in Indians and other Asians, which is the opposite of what is found. As for the Europeans, if we assume a mutation rate of 1 in 100,000 per gene per generation, we would expect roughly 0.6% of the population to possess a single defective copy in the absence of any advantage. Cholera first appeared in Europe around 1820, approximately eight generations ago. An increase due to a selective advantage of 2.3% over eight generations would result in 0.72% having a single defective copy, a far cry from the 4.3% who actually have it. Assuming 20 years per generation, a selective advantage of 2.3% would need around 1,700 years to produce the level of 4.3% seen today.
The collapse of the Roman Empire and the ensuing decline in hygiene all over Europe fits the needed time scale rather well. This event would have resulted in the spread of many diseases, such as typhoid, bacterial dysentery, and rotavirus. Like cholera, these all share diarrhea as a symptom and are spread by contamination of water with human waste. Recently, the connection between typhoid and cystic fibrosis has been strengthened. It has been found that the typhoid bacterium uses the cystic fibrosis protein when it first enters cells of the gut lining on its way to invade the bloodstream. Thus, a defective cystic fibrosis protein specifically keeps typhoid at bay and generally reduces diarrhea. Typhoid, which has a fatality rate of 10% to 20%, was endemic throughout preindustrial Europe. Remember that infant mortality was well over 50% for much of this period, and perhaps half of these infant deaths were due to diseases causing dehydration via diarrhea. Survival of infants rather than adult casualties would have driven the selection for the cystic fibrosis mutation.
How did disease affect the rise of Rome?
It has often been suggested that malaria played a significant part in the fall of the world’s greatest civilization, the Roman Empire. But before we deal with its fall, let’s consider some biological factors involved in the empire’s rise to greatness.
The Romans had two great virtues, discipline and pragmatism. The first contributed to the most effective military organization of ancient times. The second was expressed in their civil engineering. The Romans are remembered for their legions and their roads. But they also built a wide range of structures concerned with water: reservoirs, aqueducts, canals, irrigation channels, public baths, sewers, and many miles of water pipes.
Improved water engineering had two major biological effects. Better irrigation allowed the Romans to grow more food per acre and to support a greater population density. Moreover, by providing clean, fresh water and by building public baths and sewers, the Romans greatly reduced the impact of infections that are carried by contaminated water or human waste. Consequently, their population was healthier and they lost fewer victims to disease than their less hygienic competitors. More people meant more recruits for the legions. More soldiers meant more conquests and more land to irrigate. And so an upward spiral continued until other negative, biological factors limited it.
Increased population density is a biological factor that at first seems unfavorable. Consider a society that has progressed to crowding together a large number of people into growing cities that are significantly larger than neighboring communities, such as Babylon, Nineveh, Athens, or Rome. Any passing epidemic will spread more efficiently through the crowded city than in the towns and villages of more sparsely populated neighbors. Sooner or later, any such overcrowded city will be struck by pestilence. Its population will be decimated, and for a while it will be vulnerable. However, provided that it survives and recovers, its population will now consist of those who are resistant to the plague of the day. In other words, denser populations will be the first to evolve resistance to those infectious diseases that are current in their region of the world.
The next time a major conflict occurs, the movements of armies and of refugees will distribute any available infectious diseases around the war zone. The enemies of the big city-state, from smaller towns and villages, will have built up less resistance than the population of the largest city. Voilà! Infection will do most of the dirty work: The enemy will be devastated by whatever plague is in circulation, and the bigger city will gain a massive advantage. Cleanliness might be next to godliness, but the demons of disease fight on the side with the denser population.
But how can we have it both ways? First, not all diseases are spread by water or human waste, so improved hygiene from civil engineering still leaves plenty of scope for insect-borne scourges such as bubonic plague, typhus, or malaria, and for airborne diseases such as measles or smallpox. Second is the matter of temporal sequence—Rome was not built in a day. Early in its history, Rome was indeed struck by several epidemics whose nature is unknown to us because the records are fragmentary and give little clue to the symptoms. Though devastated, Rome pulled through.
Overall, a fine balance must be struck between the advantages of a disease-resistant population and a plentiful supply of healthy manpower. Consequently, great empires are few and far between. Nonetheless, when a major population center does gain a lead over its competitors, such biological factors make it extremely difficult to overthrow. Despite this, all good things eventually come to an end. As population density continues to grow, the pendulum swings back in favor of the spread of infectious disease. Sooner or later, the invisible legions of microorganisms make a comeback. In the case of Rome, this was much later and did not happen until the exhaustion of natural resources and resulting environmental damage gave infectious disease a helping hand.
How much did malaria contribute to the fall of Rome?
In ancient times, malaria was endemic in large areas of Italy, Greece, the Middle East, and North Africa, all of which were incorporated into the Roman Empire. Although we often think that ancient peoples had little idea of what caused disease, this is not entirely fair. Roman author Marcus Varro theorized that malaria was due to “tiny animalcules” that multiply in marshy places, float in the air, and sneak into people by the mouth and nose, causing fever and sickness. He was not wholly correct, yet he came close. Other Romans realized that the annoying insects that breed in marshes helped spread disease. Varro’s real problem was not so much ignorance as having no way of proving his assertion. More than a millennium later, Western technology developed microscopes capable of seeing Varro’s animalcules. And so those who thought that diseases were the result of God’s displeasure, night air, or vapors from decaying garbage often dominated public opinion.
Did malaria really promote the downfall of the Roman Empire? Granted, the Roman Empire took a heavy toll from malaria, but so did all other ancient cultures inhabiting the coastal regions of the Mediterranean basin. Unlike bubonic plague or smallpox, malaria does not occur in epidemics that sweep through a civilization, leaving massive casualties over a relatively brief time span. Malaria is an endemic disease and takes up permanent residence in an area whose inhabitants are, therefore, subjected to continuously recurring infections. The disease takes a continual heavy toll not only on life, but also on vigor. In areas where malaria is endemic, the heaviest casualties are among the newborn. Adults quite often survive the disease but are seriously debilitated and frequently fall ill again from recurrent attacks.
Evidence from corpses reveals that malaria has been present in the eastern Mediterranean region since Neolithic times. Typical Egyptian mummies had their abdominal organs removed. However, mummification was developed gradually, and some of the earliest Egyptian mummies, which date to before the abdominal organs were removed, have large swollen spleens, symptomatic of malaria. Sometime in the fifth century B.C., malaria arrived in Greece, and by the next century, it was the most common serious disease. During the fourth century B.C., malaria moved into the marshlands near Rome. The Romans responded by instituting the worship of Dea Febris (Goddess of Fever). In addition, the Romans began recruiting soldiers for the legions from mountain areas free of malaria.
Three main ecological factors worked together to undermine classical civilization: deforestation, soil erosion, and the formation of marshlands. Heating, cooking, and smelting metal ores all consumed large amounts of wood. The grazing of livestock, especially goats, prevented the regrowth of shrubs and trees, making matters worse. Although they planted olive groves and fruit trees, the Greeks and Romans made little attempt to replace the forests used for fuel. Consequently, the growing population of the Roman Empire destroyed the bulk of the Mediterranean forests. This, in turn, led to massive erosion of the soil on the exposed slopes. As upland areas became less fertile, productivity fell. The soil swept downstream by rivers was deposited in more level areas, especially around lakes and at river mouths. There it formed flat, poorly drained marshlands that allowed mosquitoes to breed, thus spreading malaria. Although alluvial deposits provide good, rich farmland, the presence of malaria drove away many of the farmers. Those who stayed suffered constant debilitating attacks. Malaria is almost never totally eliminated from the body, and exertion can bring on subsequent attacks. Those who stayed either avoided hard work because it triggered renewed bouts of malaria or worked hard and fell victim to further attacks. Either way, agricultural productivity declined.
The refugees, who left the land, fled to the cities, where they relied on the grain handouts the government provided to the urban poor—the famous “bread and circuses.” This problem was exacerbated by the land-reform policies of Roman populists such as Julius Caesar, who distributed land to retired legionaries with little experience in farming. By the time of the first emperors, Italy could no longer feed itself and Rome had become dependent on grain imported from the fertile Nile valley, which explains why controlling Egypt and North Africa was of such critical importance to the Romans. Of course, the densely populated valley of the Nile was also the channel by which diseases emerging from sub-Saharan Africa found their way into the Roman Empire.
Uncivilized humans and unidentified diseases
The rising numbers of urban poor and the consequent overcrowding provided opportunity for the spread of epidemic diseases. These were not long in making an appearance. Several major epidemics struck the Roman Empire in the first half of the first millennium A.D. The identities of these diseases are uncertain, until the Great Plague of Justinian (540 A.D.), which was almost certainly bubonic plague. The succession of epidemics gradually depleted the manpower needed for both the legions and the economy. Eventually, the empire became too depopulated to defend itself.
Why is it so hard to be sure of the identity of ancient epidemics? One issue is that ancient writers were often more worried about the effects of the pestilence and its religious implications than in accurate scientific diagnosis. Less obvious is that many diseases change over time or even go extinct, as discussed in Chapter 3, “Transmission, Overcrowding, and Virulence.” Thus, even when described thoroughly, ancient plagues might be unrecognizable today. Despite this, historians often feel obliged to name the epidemic, almost always choosing a well-known modern disease.
For example, the first major epidemic to strike imperial Rome occurred in 79 A.D., just after the volcano Vesuvius erupted, and was largely confined to Italy. Guesses have included virulent malaria or anthrax. Neither makes any real sense. Recently, genuine evidence has come to light. Examination of bodies buried alive by the volcano has shown symptoms of brucellosis. Moreover, we know that the Romans used milk from sheep and goats without, of course, sterilizing it. Even today, various strains of Brucella, some virulent in humans, are found in sheep and goats and their milk and cheese.
The next was the plague of Orosius in 125 A.D. This started with a famine caused by locusts eating the crops in North Africa. The plague itself also began in North Africa and moved from there to Italy. The identity is uncertain. Whole villages and occasional towns were wiped out and abandoned.
The plague that started in the Middle East in 164 A.D. is named either after Antoninus, emperor when it began, or Galen the physician. Soldiers from Syria brought the disease back to Rome in 166 A.D. Corpses were removed from Rome by the cartload. The plague swept through the empire until 180 A.D. and, as a final blow, killed the emperor, Marcus Aurelius. After a brief respite, the plague returned in 189 A.D. This epidemic was the first to cause a break in the Roman defense perimeter. Before this, the empire continuously expanded and was able to hold its frontiers. In 161 A.D., a horde of Germanic barbarians, the Marcomanni, left Bohemia (now in the Czech Republic) and assaulted Italy from the northeast. Disruption from the epidemic left the Romans incapable of counterattacking until 169 A.D. Reports of the conflict suggest that most of the dead Marcomanni were actually killed by disease spread by the Roman legions.
The most famous physician of Roman times, Galen, fled from Rome during this plague. He also left a description of its symptoms. High fever, inflammation of the mouth, and diarrhea were followed by eruptions on the skin, although many died before this stage. One unproven and unlikely theory is that this was the first smallpox epidemic to hit the West. This hypothesis suggests that a smallpox outbreak in Mongolia set the Huns in motion. The Huns then both infected and displaced various Germanic tribes, who, in turn, infected the Romans. However, the Marcomanni apparently caught the plague from the Romans, not vice versa. Moreover, if the Huns and Germans had been decimated first, it is hard to see them applying much serious military pressure on their neighbors. Furthermore, the course of the epidemic does not resemble later, better-known European smallpox epidemics.
Next came the great plague of Cyprian in 250 A.D. Cyprian was the bishop of Carthage, in North Africa. He described violent diarrhea, vomiting, fever, ulcerated sore throat, and gangrene of the extremities. No rash or skin eruptions were noted, and the identity of the disease remains obscure. This was a true pandemic, spreading from Africa throughout the known world and lasting for some 16 years. It moved rapidly, both by person-to-person contact and on clothes or personal articles used by its victims. It was more virulent than previously recorded diseases, killing more than half of those who were infected. Panic followed pestilence, and refugees fleeing their homes spread the plague. Large areas of Italy were left uncultivated, and the empire was weakened by loss of manpower. By 275 A.D., the empire had retreated to the Rhine and the Danube, abandoning Transylvania and the Black Forest region. The emperor, Aurelian, took the unprecedented step of fortifying Rome itself.
Over the next couple centuries, successive epidemics, probably of the same disease, ravaged the Roman Empire. Barbarian attacks intensified, especially from the Goths and Vandals. A downward spiral of pestilence, famine, and war led to the decline and collapse of the Western part of the empire. Accurate records became few and far between as civilization fell apart. The collapse took longer than might have been expected because the Romans infected the incoming barbarians, whose hordes were thinned out by pestilence, too. In 447 A.D., Attila the Hun was approaching Byzantium, capital of the Eastern Roman Empire, when pestilence “of the bowels” (perhaps dysentery of some sort) broke out among his army. The Hun army was not destroyed, but the campaign was abandoned. In 452 A.D., as Attila approached Rome, there was a repeat performance and the Huns were halted by what was presumably the same disease.
Sometimes disease struck the barbarians after they had defeated the Romans. For example, the Vandals, who had taken control of Rome’s northern African territories, were so devastated by a plague in 480 A.D. that they were swept away by the Moors, a nomadic Arab people. In 539 A.D., the Goths and Byzantines were fighting for control of Italy when the Franks burst in, hoping to take advantage of the confusion. According to the Byzantine chronicler Procopius, the Franks succumbed to the Italian secret weapons: dysentery and diarrhea.
For those who like economic theories, we should point out that the two great plagues of 164 A.D. and 250 A.D. led to the collapse of the Roman fiscal system. As is usual, casualties from the epidemics were heaviest among the poor. The ratio of peasants and laborers declined relative to the upper classes. The colossal die-offs thus eroded the tax base. In an attempt to maintain public spending on roads, irrigation, and other public works, as well as pay the legions, taxation rates were increased. This led to poverty and destitution among the surviving lower orders. Malnutrition and poorer housing resulted, which raised susceptibility to infection. A downward spiral of overtaxation, epidemic infection, and underpopulation thus set in.
Bubonic plague makes an appearance
In the East, the Roman Empire developed into the Byzantine Empire, based on Byzantium (Constantinople). The Byzantines fantasized about retaking the Western territories, especially Rome itself. The emperor Justinian (527–565 A.D.) came closest. After successful wars on his other borders, he invaded the West in 532 A.D. He retook North Africa, Sicily, Italy, and even part of Spain. If merely human enemies had opposed him, Justinian would have probably succeeded. But just as he was preparing to invade Gaul, another foe emerged: bubonic plague.
Vague accounts suggest that bubonic plague might have afflicted the Egyptians, Philistines, and other Middle Eastern nations since 1,000 B.C. or earlier. However, Justinian’s plague was the first outbreak of bubonic plague described in sufficient detail that we are sure of its identity. To the physicians of Byzantium, it was a novel and terrifying disease. Desperate to understand its cause, they performed autopsies on some of the victims. They found what they called “anthraka,” the hardened remains of lymph nodes. Our word anthracite, a type of coal, comes from the same root and reminds us that bubonic plague was called the “Black Death” because the swellings turned into hard black lumps.
Fever was followed by the appearance of buboes, black swellings in the groin and armpits due to swollen lymph nodes. Death typically occurred on the fifth day, sometimes sooner and sometimes later. Procopius, archivist to Justinian, correctly records that bubonic plague was not directly contagious and that outbreaks began on the coast. Today we know that bubonic plague is carried by fleas, which, in turn, are carried by rats. The rats spread from country to country by ship, so the plague spreads from the ports inland. Because infection is by fleabite, those who came in direct contact with plague victims were no more likely to be infected than others within range of the fleas.
The plague of Justinian began in 540 A.D. in Egypt. It spread through the Middle East and, from there, to the rest of the known world. It struck Byzantium itself in 542. As is typical for bubonic plague, the mortality was low at first and then rose steeply. The inhabitants of Byzantium died faster than graves could be dug for them. The towers of fortresses were filled with corpses left to rot, and ships were loaded with bodies and abandoned at sea. The plague circulated till around 590 A.D. Many villages and towns were depopulated. The Moors retook North Africa, the Goths retook Italy, the Persians sacked Antioch, and the Huns nearly took Byzantium itself. The population losses from Justinian’s plague took some 200 years to recover. During this period, the Islamic Empire established itself. The Byzantines and Arabs first clashed in the late 620s, while the Prophet Mohammed was still alive. After Mohammed’s death in 632, fighting continued until 718, by which time the Islamic Empire had stripped Byzantium of the Middle East, North Africa, and Cyprus. The Byzantines believed this was divine retribution for the sins of the Christians. Doubtless the Moslems agreed!
The empire was at a serious disadvantage compared to the nomadic barbarians. The citizens of the empire were crowded closer together into towns and cities. In addition, sewers and drains provided the rats with ideal channels of distribution within every major town. Although their assembled armies were susceptible to infection, the barbarian population was spread thinly over more rural areas. Moreover, many barbarians were nomadic, moving frequently and living in wagons or tents. These provided far less opportunity for rats than permanent towns and cities. Thus, the empire ran out of recruits, while the barbarians still had plenty of men to draw upon.
By the time of Justinian’s death, Rome was little more than a ghost town in the middle of malaria-infected marshland. The darkness had fallen. Not until the nineteenth century would civil engineering provide hygiene as good as that of imperial Rome. Even after the empire had retreated from many outlying areas, pestilence continued to take its toll. Thus, Roman-style culture continued locally in Britain for a hundred years or more after the empire pulled out. Continuing outbreaks of bubonic plague starting in the mid–fifth century and extending over the next hundred years were a major factor in the collapse of this and other briefly lived successor cultures.