The Course of Empire: Destruction by Cole Thomas (1836)

Plague, Climate Change, and the End of Ancient Civilizations

By Daniel Stein

 

Periodically, civilizations collapse. Whether through war, disease, famine, or internal strife, complex societies can rapidly vanish, leaving the survivors to start a process of rebuilding that can take centuries. “A society has collapsed,” writes anthropologist Joseph Tainter, “when it displays a rapid, significant loss of an established level of social complexity.” These events often mark the transition between historical eras. The collapse of Bronze Age civilization in the Eastern Mediterranean between the thirteenth and twelfth centuries BC led to a brief “Dark Age” and then the beginning of the Iron Age. The collapse of the Roman Empire set the stage for the Middle Ages. The speed with which these events can occur sometimes leaves modern scholars at a loss to explain what happened. Why do some societies collapse while others succeed? Why does a society which survives serious threats at one period of its history collapse when it faces the same threats later on? What makes a society vulnerable to collapse? As fears of climate change become increasingly widespread today, some researchers have proposed environmental causes for the demise of ancient civilizations. They see this as a precedent and warning for our society’s current struggle with climate change. This essay will look at the relationship between the environment and the collapse of ancient states.

Various sources provide evidence about the ancient climate. Ancient writers sometimes comment on the environment, especially natural disasters like storms, droughts, volcanic eruptions, and other natural agents like epidemics. A letter written by the Hittite king Mursili II (1321–1295 BC) laments: “the land of Hatti has been sorely, greatly oppressed by the plague . . . Behold, it is twenty years since people have been continually dying in the land of Hatti. Will the plague never be eliminated from the land of Hatti?” In his sermon “In Time of Famine and Drought,” St. Basil the Great of Caesarea (330–379 AD) declared to his congregation: “Brothers and sisters, we see how the heavens have grown hard and unyielding, naked and bereft of clouds . . . The earth is completely dried up, terrible to see, barren and utterly unsuitable for planting.” The second-century AD Roman astronomer and mathematician Ptolemy of Alexandria reported the number of rainy days per year in his Phases of the Fixed Stars. Perhaps the most famous observer of a natural disaster is Pliny the Younger (61–113 AD), who lived through the eruption of Mt. Vesuvius in 79 AD and left a description of the event in his letters. Based on sources like these, one group of researchers compiled a list of all recorded weather events between 100 BC and 800 AD to study the role of climate fluctuations in the history of the Roman Empire.

Scientific methods are a more reliable source of evidence about the ancient climate. DNA analysis of human teeth dating to the early Bronze Age (3000–1800 BC) showed the earliest evidence for the bacterium Yersinia pestis, the source of plague, providing a natural agent that could have influenced demographic change and population movement. In terms of climate, cave mineral deposits called speleothems can be dated using radiocarbon or uranium-thorium dating, and chemical analysis of oxygen (δ18O) and carbon (δ13C) isotopes—as well as the size of speleothem rings—can be used to measure variations in rainfall, temperature, vegetation, and major climatic events. Using similar chemical/isotopic analysis, lake and marine sediment cores also give evidence for changes in effective moisture availability. Ice cores can be dated by layer and preserve evidence of volcanic eruptions and atmospheric concentration of certain elements. Tree ring sizes show fluctuations in average annual temperatures. Pollen samples give a profile of vegetation patterns for a certain time, providing evidence for human agriculture and “rural land-use change.” (Nevertheless, historians should be cautious when basing conclusions on pollen samples. Since pollen data are affected by humans and have traditionally been reported as percentages and not as absolute values, it is hard to distinguish climatic effects from human effects. Researchers must also be aware that any positive increase in one type of vegetation will automatically lead to a negative “correlation” with other types of plants.) Overall, these techniques have allowed scientists to reconstruct “climate series” that track environmental changes over time. Scientists can then compare these series to the historical record to see if there is any correlation between the climate and human events.

Was climate change responsible for the end of the Bronze Age? After flourishing for hundreds of years with extensive trade and diplomatic contacts, the Bronze Age civilization of the Eastern Mediterranean suddenly collapsed. Most of the Mycenaean palaces were violently destroyed around 1200 BC. The old hierarchy of kings, warriors, priests, and local officials disappeared, along with the Linear B writing system. Bands of marauders known as the Sea Peoples sailed along the coast of Asia Minor and the Levant, sacking cities. A tablet from the last year of the Greek palace of Pylos conscripts men for duty as “watchers on the coast,” suggesting a fear of invasion. As trade routes failed, Hittite kings tried desperately to maintain their supplies: “You must furnish them with a large ship and a crew, and they must transport the grain to their country . . . You must not detain their ship!” The pharaoh Merneptah recorded that he had “caused grain to be taken in ships, to keep alive this land of Hatti.” Writing to the king of Cyprus, the king of Ugarit lamented: “my cities were burned, and they did evil things in my country . . . the country is abandoned to itself.” Within a few decades, the crisis was over. The Hittite empire disappeared, as did the Mycenaean palaces and most other Bronze Age powers. As one writer put it, “the major empires of the Late Bronze Age . . . seem to have evaporated as quickly as moisture on a hot afternoon.” Egypt defeated the Sea Peoples but never again attained the same level of prosperity or influence. The demise of Bronze Age empires opened the way for the Iron Age and the rise of new powers like Phrygia and the Neo-Assyrian Empire.

There is evidence that climate shifts may have contributed to the end of the Bronze Age. One study of the palace at Pylos concludes that “a brief period of drier conditions around 3200 yrs BP [ca. 1250 BC] may have disrupted the Mycenaean agricultural system,” while increasing aridity in the years after the palace’s destruction “probably reduced crop yields and helped to erode the basis for the reinstitution of a central authority and the Palace itself.” On a larger scale, analysis of fossilized pollen grains concluded that “the driest event throughout the Bronze and Iron Ages occurred ~1250–1100 BCE,” followed by a “dramatic recovery in the Iron I,” which led to “settlement recovery.” Scholars David Kaniewski and Elise Van Campo conducted their own pollen analysis and concluded, “the LBA [Late Bronze Age] crisis coincided with the onset of a ca. 300-year drought event 3200 years ago. This climate shift caused crop failures, dearth and famine, which precipitated or hastened socio-economic crises and forced regional human migrations at the end of the LBA in the Eastern Mediterranean and southwest Asia.” Oxygen-isotope analysis of speleothems at the Soreq Cave in northern Israel suggests a period of low annual precipitation between the Bronze Age and Iron Age, while pollen cores from Lake Voulkaria in western Greece show that local plants were adapting to a new arid environment. In 1177 B.C.: The Year Civilization Collapsed, archaeologist Eric Cline suggests the possibility of “earthquake storms” caused by a series of sequential shifts along a fault line. He cites evidence of late Bronze Age earthquakes at Mycenae, Pylos, Tiryns, Midea, Thebes, Kynos, Lefkandi, Kastanas, Korakou, Profitis Elias, and Gla in Greece; Troy, Karaoglun, and Hattusa in Turkey; and Ugarit, Megiddo, Ashdod, and Akko in Syria and Israel. The evidence for earthquakes at Mycenae and Tiryns includes crooked walls and unburied bodies. Combined with reports of famine and supply shortages (“I have no grain in my lands,” wrote one Hittite queen to Rameses II), this may have destabilized Bronze Age states and driven the migration of groups like the Sea Peoples.

Building on this evidence, some have argued that the root cause of the Bronze Age collapse was the environment. One group of researchers argues, “We believe the domino effect . . . cold spells, droughts and famine in the north, causing groups to invade sedentary lands in the south—explains the Late Bronze collapse.” Another group says, “The abrupt climate change at the end of the Late Bronze Age caused region-wide crop failures, leading towards socio-economic crises and unsustainability, forcing regional habitat-tracking [population movement to habitable areas].” According to Professor Brandon Drake of the University of New Mexico, “A sharp increase in Northern Hemisphere temperatures preceded the collapse of Palatial centers, a sharp decrease occurred during their abandonment . . . These climatic changes could have affected Palatial centers that were dependent upon high levels of agricultural productivity. Declines in agricultural production would have made higher-density populations in Palatial centers unsustainable.” In other words, whether or not climate was directly responsible for the collapse, these scholars argue that climate was the ultimate source of the problems that ended the Bronze Age.

A similar argument can be made for the other major collapse of antiquity: the fall of the Roman Empire. In The Fate of Rome: Climate, Disease, and the End of an Empire (2017), Kyle Harper argues that Rome reached the peak of its prosperity and extent during the Roman Climate Optimum (200 BC–150 AD), followed by a Late Roman Transitional Period (150–450 AD) and the Late Antique Little Ice Age (450–700 AD) during which a steadily deteriorating climate and a series of plagues gradually destroyed the empire. As climate researchers note, between the third and seventh centuries AD, regions including Anatolia, the Aegean, the Black Sea, Syria, and even the Negev desert enjoyed an extended period of “late antique prosperity”—defined by increased numbers of settlements, agricultural expansion into previously uncultivated areas, and population growth. They then entered a rapid decline (eighth to ninth centuries) as once-flourishing lands were abandoned and turned into deserts. There are 106 recorded sites in the Upper Galilee during the Hellenistic period, 170 in the Roman period, 194 in the late antique period, and then only thirteen for the early Islamic period, suggesting a “dramatic decline . . . during the 7th–8th c. AD.” According to one group of researchers, “it seems that the previously homogeneous and prosperous rural world of the late antique Eastern Mediterranean more or less collapsed across the central zone stretching from Gaza to Cappadocia” following the seventh century. Another group explains that there is “a steady increase and peak of settlement numbers in the Roman and Early Byzantine periods, followed by a significant reduction of Middle Byzantine evidence. These changes are consistent with data from across the Eastern Mediterranean and are frequently hypothesized to result in part from changing climatic and environmental conditions.” So many settlements were abandoned that they have become known collectively as the “dead cities of northern Syria.”

Was the climate to blame? In a study of climate and settlement in southwest Anatolia, Jacobsen et al. concluded that climate “may have some responsibility” for depopulation and settlement contraction and abandonment in the sixth and seventh centuries AD. Weather conditions after 460 AD shifted from wet to arid, with the minimum annual precipitation between 570 and 590. In 536, a major volcanic eruption left a twelve–eighteen month dust veil over the northern hemisphere, leading to environmental cooling and a “536–550 CE climate downturn.” There is also evidence for a larger pattern of cooling from 450–800 AD, which has been labeled the Dark Ages Cold Period (DACP) and may have lowered agricultural productivity. The authors are careful to note, however, that “there were earlier instances of dry climatic conditions where the local population appears to have been relatively unafflicted, or even to have prospered.” 

In addition to possible climate change, the Roman Empire was struck by a series of major epidemics. The Antonine Plague (165–180 AD), brought back by soldiers campaigning in the East, is said to have killed between a quarter and a third of the empire’s population. At the height of the plague, the historian Dio Cassius estimated that 2,000 people were dying per day in Rome. A century later, the Plague of Cyprian (250–270 AD), named after the bishop who described its symptoms, was said to have killed 5,000 people per day. These epidemics decimated the Roman population and made it harder to defend the empire’s borders. In 541 AD, the first major outbreak of bubonic plague, known as the Plague of Justinian, appeared in Egypt, sweeping through the empire and ravaging the population over eighteen successive waves during a period of 200 years until 755. The Byzantine historian Procopius called it “a pestilence by which the whole human race was near to being annihilated,” and recent estimates have placed total fatalities between twenty and fifty million.

In short, there is evidence that climate contributed to the ending of the Bronze Age and the Roman Empire. However, it is important to be cautious when designating factors like climate change as the sole or even primary cause of a civilization’s collapse. Humans have adapted to a wide range of environments, so there is no reason to think that a shift in climate would automatically entail a collapse of society. While climate-based explanations tend to focus on periods where climate change can be associated with political crises, there are many more cases where drought, earthquakes, and epidemics did not lead to the collapse of society. As Cline notes, “We must . . . acknowledge that droughts have been frequent in [the Levant] throughout history and that they have not always caused civilizations to collapse.” The earthquakes at Mycenae and Tiryns preceded the final destruction of these sites by at least a few decades. At the Iron Age city of Gordion, a fire destroyed the citadel around 800 BC, but the inhabitants quickly recovered and rebuilt the entire structure on new foundations. The plague of Athens (430 BC) may have killed up to twenty-five percent of the city’s population, but the Athenians continued to fight the Peloponnesian War for nearly three more decades. In Asia Minor, reduced effective moisture beginning in the fifth century led to “urban water infrastructure adaptations,” which helped save and distribute water more effectively. Theories about historical climate change may give too little credit to human resilience and ingenuity. 

Recent critiques have identified a number of issues with current models of human-climate interaction. According to Jacobsen et al., there are “significant and recurring issues” with these studies, including “correlation-based conclusions that lack convincing causal explanations,” “a bias towards periods of ‘crisis’ which mischaracterizes human-environment interactions,” and “a focus on large regions without high-quality comparative data sets.” A comprehensive review published in Nature found many of the same problems. The authors note that “populations survived—and often thrived—in the face of climatic pressures,” citing numerous cases where society adapted to make the best use of a changing climate and concluding that “the overwhelming focus in HCS [History of Climate and Society] on crisis and collapse misrepresents the character of historical interactions between humanity and climate change.” As they note, proxy-based climate reconstructions (i.e., reconstructions based on evidence like pollen or speleothems) are often imprecise and represent an average of conditions over decades or even centuries. They are not a direct record of climate conditions but rather a product of “statistical interpretations of available sources,” which makes it difficult to prove a connection between climate and historical events or even compare data for different time periods. They also ignore high levels of climatic variability within broader periods of climate change. Moreover, “the basic assumption that higher temperatures and water availability will facilitate higher agricultural productivity is too simplistic.” So when looking for the causes of a specific collapse, researchers should use environmental data with caution and look for other non-environmental causes before reaching broad conclusions.

Bronze Age sources are so limited that it is difficult to know what specifically caused depopulation or the migration of the Sea Peoples or who the Sea Peoples were in the first place. Aside from climate, the Bronze Age collapse may have been caused by the invasion of Dorians from the north or by internal tensions within the palace system, or more likely by a combination of factors with the climate playing a role. For the Eastern Roman Empire, there are clear non-environmental factors that explain the collapse. The Byzantines had fought a long and exhausting war with the Sassanian empire (Iran) during the fifth and sixth centuries AD, followed by an equally destructive invasion of Muslim armies during the seventh century. The evidence for a “Roman Climate Optimum” from the second century BC to first century AD is weak to nonexistent. While the environment may have contributed to the decline and collapse of the Bronze Age empires or Rome, it is unlikely that this was ever the sole or even primary factor in the fall of ancient civilizations.

 

Daniel Stein (College ‘25) is a student at the University of Pennsylvania majoring in Neuroscience and Classical Studies. He is the Lead Research Editor for Discentes.

 

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