The Science of Roman History

Biology, Climate, and the Future of the Past

Walter Scheidel, Walter Scheidel

• Publisher: Princeton University Press
• Year: 2018
• ISBN:
  9781400889730
• Topic: Historia
• Subtopic: Historia antigua romana

How the latest cutting-edge science offers a fuller picture of life in Rome and antiquity This groundbreaking book provides the first comprehensive look at how the latest advances in the sciences are transforming our understanding of ancient Roman history. Walter Scheidel brings together leading historians, anthropologists, and geneticists at the cutting edge of their fields, who explore novel types of evidence that enable us to reconstruct the realities of life in the Roman world.Contributors discuss climate change and its impact on Roman history, and then cover botanical and animal remains, which cast new light on agricultural and dietary practices. They exploit the rich record of human skeletal material--both bones and teeth—which forms a bio-archive that has preserved vital information about health, nutritional status, diet, disease, working conditions, and migration. Complementing this discussion is an in-depth analysis of trends in human body height, a marker of general well-being. This book also assesses the contribution of genetics to our understanding of the past, demonstrating how ancient DNA is used to track infectious diseases, migration, and the spread of livestock and crops, while the DNA of modern populations helps us reconstruct ancient migrations, especially colonization.Opening a path toward a genuine biohistory of Rome and the wider ancient world, The Science of Roman History offers an accessible introduction to the scientific methods being used in this exciting new area of research, as well as an up-to-date survey of recent findings and a tantalizing glimpse of what the future holds.

CHAPTER ONE

Reconstructing the Roman Climate

Kyle Harper & Michael McCormick

Climate and the Science of Antiquity

Environmental history, as a subfield, is now more than a generation old. Traditionally, it has focused on the changing relationship between human societies and the natural world, in both physical and biological dimensions. It has overlapped and connected with related fields such as agrarian history, landscape archaeology, geography, and the study of historical demography and infectious disease. From Braudel to Horden and Purcell, the labors of environmental historians have yielded a much clearer understanding of both the enabling power of the natural world and the constraints it imposes. At the center of the field, it might be suggested, has been an effort to describe how the imperative of extracting energy from the environment has shaped human societies and how, in turn, human societies have exploited and reshaped physical and biological environments in their search for fuel, food, and water.

In the case of Rome, environmental history has built on the traditional study of “the Mediterranean” as a geographical and ecological region.¹ The need to understand the particularities of the zone at the core of the Roman Empire has been primary. From there, study has branched into the exploration of ancient food production, with work spanning from the history of specific crops to the classic work on famine and food shortage by Peter Garnsey.² Water systems—from rural irrigation to the monumental urban hydraulics—have often figured prominently in the study of the Roman environment, given the delicacy of water management in the many semiarid regions of the Empire.³ Forests were once a major theme and are becoming so again, as historians consider how the Romans met their voracious demand for fuel and construction materials.⁴ Soils, too, once received attention from historians, although interest has unfortunately abated in recent decades.⁵ Human biology has occasionally been placed at the center of environmental history, for instance in the work of Walter Scheidel or Brent Shaw on disease and mortality, or the contributions of Robert Sallares on the history of malaria.⁶ In short, ancient environmental history has sought to fulfill the challenge issued by the Annales school to write histoire totale—to consider human societies in all their material dimensions.⁷

Perhaps the area where the “science of antiquity” is most dramatically changing our understanding of the ancient environment is the study of the paleoclimate.⁸ In the last decade or so, climate history has been revolutionized by the discovery and synthesis of new data from unexpected sources. Partly as a by-product of our urgent need to understand anthropogenic climate change, the recovery of paleoclimate records—allowing reconstruction of natural climate variability and change into the deep past—is a boon to the enterprise of environmental history. The global climate system, at some level, frames all the systems and mechanisms that are of concern in environmental history. Where we previously knew next to nothing for ancient history about the backdrop of climate change, recent and ongoing scientific investigations have begun to pierce the veil and illuminate the underlying conditions in which ancient societies developed. The importance of climate in a traditional society is easy to grasp, particularly in societies enmeshed in the favorable but predictably unpredictable precariousness of the Mediterranean.⁹ So is the scholarly delicacy of demonstrating precise and rigorous causal connections between environmental conditions and historical change.¹⁰

In exploring the impact of climate change on ancient societies, and the responses of those societies to the environment, it is essential to state at the outset that both climate change and social impact are complex and multidimensional phenomena that usually cannot be reduced to unilinear cause and effect. Climate change can take many different forms, each with impacts that may differ depending on the circumstances and resilience of the society that experiences them.¹¹ Changes that have negative consequences in one region may affect other regions more positively. With respect to both temperature and precipitation, it is not only the absolute amount of variation that matters. The timing of these variations could be more or less favorable to particular crops and animals in particular places. Extreme variations could be negative as well as positive: too much wetness can promote blights of crops and animal disease. Speed of change counts as much as timing. In general, slow and gradual climate change is considered less damaging because farmers and pastoralists could adapt to it more easily. The nature of change itself can play a role: unidirectional, or fluctuation back and forth, and fluctuation at different rhythms can modify how climate change affects society. Finally, the clustering of climate events or change can make a big difference. Given the built-in precariousness of the Mediterranean environment, ancient societies developed methods of stocking foodstuffs for the inevitable bad years. But when bad years clustered together, two, three, or more bad years in a row could menace even the most resilient and well-stockpiled of ancient societies. Fluctuation could be as dangerous as unidirectional change.

The resilience of ancient societies likely also changed historically. One of the major “structural” components in Mediterranean resilience was the exceptional agrarian productivity of the Nile valley.¹² Beyond the productivity itself, it was essential that this productivity was determined by factors arising in an Indian Ocean climate system distinct from the prevailing North Atlantic climate that dominates the rest of the Mediterranean basin.¹³ Even if general conditions in the Mediterranean were unfavorable for a given harvest, there was a good chance that those conditions would not affect Egypt’s harvest. So long as Egypt’s food production was integrated into the general Mediterranean economy, and the shipping and distribution systems existed to move that food as needed, much of the Mediterranean was likely resilient against temporary climate-induced shortfalls. Other layers of resilience included the development of interconnected markets around the Mediterranean and the shipping to service them, and the construction of massive granaries, at least for the great cities, to stockpile grain for the inevitable bad years.¹⁴ Such granaries certainly sustained Rome and its ports, as well Constantinople, including Tenedos, on its sea approach.¹⁵ The development of sophisticated water storage and delivery technologies was another important component of resilience in an arid Mediterranean environment. There is a strong case that the aqueduct of Carthage was built in response to a five-year drought that ended in 128 CE; a severe drought explicitly triggered the emperor’s decision to rebuild that of Constantinople in 766 CE.¹⁶ Justinianic attention to waterworks in the Holy Land seems similarly to reflect a significant drought.¹⁷

Until very recently, we had only a few written sources, in combination with archaeological evidence, to reconstruct the history of the ancient climate, and these did not take us very far. With the exception of the Nile floods—which must be reconstructed usually from indirect evidence—antiquity is generally lacking in long series of historical or other reports that would allow us on their own to detect shifts in climate. H. H. Lamb nevertheless did a remarkable job of divining various climate trends from the most scattered and disparate evidence, and his general assessments remain worth reading.¹⁸ But even if the written evidence of antiquity is insufficient in itself to reconstruct ancient climates, judiciously used, it provides a precious check on reconstructions based on other evidence. In a few cases, it is strong enough to extend and deepen climate reconstructions based on paleoclimate proxy evidence: for instance, the great cooling initiated by the “year without sun” in 536 CE.¹⁹ Archaeological evidence will likely play an increasing role in coming years, so long as the chronological and spatial resolution of its information is sufficiently fine to permit precise correlation of cause and effect.

In the absence of direct instrumental records before the most recent generations, climate scientists reconstruct the main features of ancient climate by using proxy data. Proxy data come from tree rings, ice cores, speleothems (stalagtites), lake varves (sedimentary layers), and other natural archives.²⁰ Comparison of the physical characteristics of proxies with instrumental records of climate over the last century or so has revealed consistent relationships between certain physical characteristics and climate conditions. The assumption that those relationships and the underlying mechanisms have remained constant allows climatologists to extrapolate climate data from similar proxy signals for periods when no instrumental records survive.²¹ The rapidly growing precision and detail of the proxy data is mind boggling, and we will offer more details on their testimony below. Historians of the ancient world can be grateful for the proliferating new data and their new insights about the environmental context of ancient economies, societies, and polities.

This chapter tries to frame our current state of knowledge about the physical climate in the period of the Roman Empire’s expansion, flourishing, and final fragmentation, ~200 BCE to 600 CE. The emphasis here is on the new evidence of paleoclimate proxy data. We will explore what it is starting to tell historians about the timing and nature of large-scale climate change in the centuries of interest. A final section draws together the disparate sources of evidence into a tentative narrative, highlighting the questions that can be asked about the relationship between climate change and historical change and underscoring the need for more and better data to fill in such a narrative in the future.

Roman Geography and Climate

Both in its scale and its internal diversity, the Roman Empire was an extraordinary geographical entity, a fact obviously relevant to its environment and wo...