Where Biology Meets History: Using Plant Remains To Understand Climate, Agriculture, and Empires

How did ancient societies feed their populations, adapt to climate changes, and cultivate their lands? John M. Marston, professor of archaeology and anthropology and director of the archaeology program at Boston University, studies ancient plant remains to answer these questions. As an environmental archaeologist, he combines his passion for biology, ecology, and history to conduct research to glimpse into how past societies interacted with their landscapes and how those decisions affected their environments. A specialist in paleoethnobotany, the study of archaeological plant remains, Prof. Marston connects ecological theory with archaeological methods to reconstruct agricultural and land-use strategies from plant and animal remains.

V: My first question is, you specialize in paleoethnobotany, the study of archaeological plant remains. What can these remains tell us about the inhabitants and conditions in the ancient world?

Prof. Marston: We can learn a lot from plant remains, which is one reason why they are so interesting to study. One of the most direct ways they tell us about ancient people is through food—what people ate, the types of food they grew, the kinds of food they gathered from the natural environment, the ways in which they prepared their food, and how the waste from the food was discarded.

We can learn so much about food and food systems through these methods.

Another aspect we can learn from paleoethnobotany is what the environment was like at that time and the

types of environmental changes that might have occurred over time. If we have a long-lived site or a series of sites that date to different periods, we can learn both how humans were deliberately using the environment at that time and how the environment changed in response to natural factors, as well as human intervention and manipulation of those environments.

These are probably the two most important aspects of plant remains, and that is one of the reasons why they are such powerful tools for reconstructing the past and understanding what human life was like hundreds or thousands of years ago.

V: Wow, it's amazing how we can learn so much from just plant remains. My next question is about the kinds of projects you have worked on in the environmental archaeology laboratory. Can you share any interesting findings?

Prof. Marston: My personal specialty is my interest in agricultural systems: how they were designed, what kinds of food they were intended to produce, how they changed natural environments as people manipulated those environments to create better agricultural conditions, and the subsequent impact of those agricultural systems on the environment.

These are the general research questions that frame my work.

I conduct this research primarily in the region between the Eastern Mediterranean and Central Asia, roughly Central Western Asia, the Eastern Mediterranean, and Southeastern Europe.

Within this broader scope, I have several projects in different countries that all aim to uncover the same central question. I study very long-lived settlements, usually cities of some kind, that persisted for hundreds or thousands of years, to understand how the inhabitants of those cities manipulated their environments, created agricultural systems, and adapted to environmental change over time, especially in response to political and economic shifts.

For example, imagine living in a small town in central Turkey (or in a town that is today in Israel) as part of a local kingdom. Suddenly, the Roman Empire arrives and conquers the region, and now you are part of the Roman Empire. You yourself have not changed, your society has not changed, and your neighbors have not changed, but you are now part of a vast political entity. How might that change the way you farm crops, the types of food you have access to, or the economic networks you participate in? And what are the environmental implications of those changes over time?

These kinds of questions are the focus of my research. Even though I work in different places, many of the same questions arise, especially in relation to large political systems such as empires, including the Persian Empire and the Roman Empire, that expanded across vast territories and encompassed this entire region.

One recent project that illustrates this type of work focuses on an archaeological site in western Uzbekistan, in Central Asia, near a body of water that used to be the Aral Sea and is now only a very small remnant because most of it has evaporated. This region is a hyper-arid desert and extremely dry, and the only way farming is possible is through water supplied by two major river systems.

Because of this, settlements historically formed along the courses of these rivers. What is interesting, however, is that the course of the river has changed over time. As a result, many of these settlements now sit in the middle of the desert, where it would be impossible to grow anything today. The reason is that the river moved in the hundreds of years since those settlements were occupied.

We conducted research at one such site that had originally been located along the river. There, we discovered evidence of a very sophisticated system of irrigated farming that existed much earlier than previously understood, based on earlier archaeological research in the region.

What this tells us is that many of the technologies and strategies people used to grow food in this challenging environment were already in place much earlier than scholars had thought. This suggests that these agricultural systems were not introduced by later political and economic systems, which were previously believed to have driven an agricultural boom in the region, but were instead developed locally on a smaller scale long before large empires arrived.

This finding tells us quite a lot about how people interact with their environments and develop innovative strategies on their own. It suggests that these developments were not simply the result of large political authorities introducing new systems, but rather the outcome of local experimentation and adaptation.

That is one example that illustrates some of these broader research questions while also offering a unique perspective on how agricultural systems developed and evolved over time.

V: That is fascinating. How did ancient societies change their agricultural practices in relation to their evolving economies and political state?

Prof. Marston: One thing I would add to the earlier answer is how these empires or territorial kingdoms function. As they expand from one area into new and different environmental conditions, they encounter very different landscapes. For example, the Roman Empire was based in Rome, and the environment in Rome is very different from the environment in what is today Iraq. Yet the empire governed those regions as well.

One of the key aspects I am interested in understanding is the extent to which there is central authority coming from the experience of living in and manipulating one particular type of environment, and how that expertise gets transferred into completely different environments with very different agricultural conditions. These places may have different rules for agriculture, different kinds of crops that can be grown, and sometimes new crops that cannot be grown in the empire’s homeland. At the same time, there may be crops from the homeland that cannot grow in the new region.

This raises an important question: to what extent are these processes centralized from the original center of the empire, and to what extent do they rely on local expertise and local knowledge in these new environments to determine what can be done locally?

What we find in almost every empire or large kingdom is that it tends to be a balance between the two. In some cases, people attempt to implement agricultural practices based on the regions they originally came from. In other cases, they rely more heavily on local knowledge and adapt to local environmental conditions.

Different empires appear to emphasize one approach more than the other. The Romans, for example, may have leaned more toward maintaining familiar agricultural practices from Italy, even when operating in very different environments. By contrast, Islamic empires that emerged roughly between 700 AD and the Middle Ages appear to have been more flexible about local environmental conditions and allowed local communities to make more independent decisions.

This represents a very different perspective from the Roman approach. As a result, we can observe interesting differences that seem to reflect the political structures of these empires. Understanding these differences more clearly is an important question for future research.

V: That's really cool. Have you found any patterns between specific social events and impacts on land?

Prof. Marston: That's a great question. One thing we can see quite clearly is that many societies living in similar environmental settings react to and work with their local landscapes and environments in similar ways.

Overall, I would say that local environmental and climatic conditions are more important in determining the types of crops people were growing than the political or economic systems they were part of. In many places, we see more continuity over time in agricultural practices than we might expect, especially considering the large-scale political changes that occurred in those same regions over long periods.

However, that is not always the case. Sometimes a new political group comes in, and we see a very different reorganization of the agricultural system. For the most part, what is possible in a given environment, along with local knowledge about what grows well there and how to cultivate those crops, tends to be the more important factor.

These factors often outweigh broader political or economic influences such as incentives, administrative changes, or tax systems. There are some exceptions to this pattern, but overall, it appears to be the dominant trend that I have observed so far.

V: Would you say that the environment affected culture and societies more than culture and societies influenced the environment?

Prof. Marston: It's a good question. I don't think there is a clear answer one way or the other. Part of the reason is that these two factors are so closely connected that it is very difficult to separate them.

For example, we live in a particular environment. Here in Massachusetts, it is cold in the winter. There are certain kinds of plants that we might want to grow, like oranges or figs, but we cannot grow them here because the winter temperatures would kill those plants. Instead, we grow other kinds of crops.

However, the crops we grow now have not always been native to this area. For example, apple trees are very common in New England, but apples originally come from Central Asia. They were brought here, but they grow fairly well in this environment, and over time, we have developed varieties that are well-suited to this climate.

At the same time, growing apple trees requires us to manipulate the environment in certain ways. The environment influences which crops we can grow, but once we decide to grow a particular crop, we also modify the landscape to support it.

For example, apple trees need a lot of sunlight. Because of this, we clear the land and plant them in orchards where no other trees are competing with them for light. There might be some grass, but generally, no other trees are growing nearby.

So, we manipulate the environment to grow this crop, but the reason we grow the crop in the first place is partly that we like it and partly because it grows well in this environment. In this way, there is a constant relationship between cultural choices and environmental opportunities. These choices then lead to further changes in the environment as people continue to manipulate it in specific ways.

Because of this close relationship, it is very difficult to say that one factor is more important than the other.

V: Got it. So, they go hand in hand.

Prof. Marston: Exactly.

V: I'm particularly interested in the impact of climate change on ancient civilizations. Based on your research, what kind of cultural adaptations did ancient civilizations pursue due to environmental and climate changes?

Prof. Marston: In the area where I work, many regions sit very close to the boundary of where productive agricultural systems can exist using only rainfall. In some of these areas, crops must be irrigated, which usually means that settlements develop along river systems where water can be distributed for farming. Areas such as the Nile Valley in Egypt and Mesopotamia between the Tigris and Euphrates rivers fall below this rainfall threshold. In those regions, crops cannot be grown using rainfall alone, so irrigation is necessary.

However, in much of the broader Middle East, it is possible to grow crops using rainfall alone, especially drought-tolerant crops such as barley or wheat. The challenge is that if climate change shifts this boundary even slightly, it can significantly change where irrigation becomes necessary and where rainfall is sufficient for farming.

One example of this is northern Mesopotamia, most of which today lies in northeastern Syria and southeastern Turkey. Over the last 5,000 years, this region has shifted back and forth several times due to major climatic changes.

In this transitional zone, we see periods when agriculture expands across the landscape. During these wetter periods, human settlements spread out more widely because people are able to farm larger areas. Instead of a few large cities concentrated along rivers, settlements become more dispersed as agriculture becomes possible across broader regions.

However, when conditions become drier, we see a contraction of settlements toward those river cities. At the same time, people shift away from crop farming and toward grazing animals. In these drier conditions, there may not be enough rainfall to support crops, but there is still enough grass that can feed sheep or cattle. As a result, communities begin to rely more heavily on raising livestock.

We can think of this as somewhat similar to ranching in the western United States. Some areas are too dry for farming but are well-suited for raising cattle. In these ancient regions, people appear to move back and forth between farming and pastoralism depending on climate conditions.

Studying areas that lie at the edge of these important climatic zones can be a very effective way to understand how climate change affects agricultural systems and social systems. We see people physically moving across the landscape, switching from one crop to another, or shifting from crop production to animal herding in response to climatic changes.

What makes this especially interesting is that we can combine archaeological evidence of these changes with climate records that tell us when rainfall increased or decreased. When we match these two sources of information together, we can begin to understand the relationship between climate shifts and human responses.

This has been particularly impressive because the evidence clearly shows how people adapted their agricultural strategies in response to changing climate conditions in these regions.

V: Interesting. So, most of the time, it's people just finding ways to adapt quickly to survive.

Prof. Marston: Yes. In some cases, it can be more technological. For example, today when an area becomes drier, we often increase water storage and expand irrigation systems to compensate for those drier conditions.

We do find periods in the past when people continued doing what they had been doing and simply added additional watering systems, such as irrigation or new canal networks.

However, for the most part, people tended to adapt in simpler ways. In many cases, it was cheaper and easier to adjust their practices or move to a different area rather than develop complex technological solutions.

V: I see. Can you share more about your current project focusing on bronze and Iron Age suburban centers?

Prof. Marston: Yes. One long-standing project that I continue to work on focuses on the Late Bronze Age and Iron Age periods in central Turkey. The project is centered on the ancient city of Gordion.

This city is interesting for several reasons during these periods. First, during the Late Bronze Age, it was part of the Hittite Empire. Later, by the end of the Iron Age, it became part of the Persian Empire, then the Greek Hellenistic empires, and eventually it was incorporated into the Roman Empire. So there are periods when the city was controlled by outside empires. However, in the earlier part of the Iron Age, it served as the capital of an independent kingdom that expanded outward from Gordion and eventually controlled much of what is today central Turkey.

What makes this political history particularly interesting is that it is paired with an environment that sits near the margin of where agriculture can reliably succeed. Throughout this entire period, the region received enough rainfall for agriculture, so farming using rainfall alone was possible. However, what varied was the level of risk involved in farming. During some periods, rainfall was consistent enough that farmers could expect a good harvest in most years. During drier periods, however, farming became much riskier, and there was a significant chance that crops could fail because of drought. Because of this, we see different strategies for adapting to these environmental conditions across different political periods. It is this intersection between environmental conditions and political change that I am particularly interested in studying.

One of the reasons Gordion is such an important site for research is that we have extensive data from it. Researchers have conducted detailed analyses of plant remains, so we know a great deal about the crops people were growing, the ways those plants were cultivated, and the agricultural systems that supported them.

We also know a great deal about animal remains because researchers have studied the bones found at the site. This allows us to understand the kinds of animals people were herding and the reasons they were raising them.

For example, sheep can be raised for several different purposes. They might be raised primarily for meat, meaning they are slaughtered once they reach a certain age. Alternatively, they might be raised for wool, in which case they are kept alive to older ages so they can continue producing wool each year. They might also be raised mainly for dairy production. In that case, many of the male sheep would be slaughtered earlier, while female sheep would be kept because they produce milk.

By studying the bones, we can often distinguish between these different strategies. When we compare this information with the plant remains, we can begin to see how farming and animal husbandry systems worked together.

From there, we can examine how these systems fit within the broader paleoclimate record and the political history of the region. This allows us to construct a detailed history of how people adapted their food systems over time in response to environmental change, political shifts, and economic conditions.

At Gordion, we have enough data to create a particularly rich and detailed picture of how people lived and adapted in this region. In fact, we can understand this city and its surrounding landscape in far greater detail than many other sites from the same general region. This makes Gordion a powerful case study for understanding larger questions. It helps us explore when political change was the most important factor, when climate change played the dominant role, and when changes people made to the landscape, either intentionally or unintentionally, had the greatest impact on agriculture.

By examining these factors across different time periods, we can see how their relative importance shifted over time.

V: I didn’t realize you could learn so much from animal remains, especially about agricultural practices during that period, when they are studied alongside plant remains.

Prof. Marston: Animal bones are really cool. They're almost as cool as plants.

V: For my last question, I like to ask everyone: what sparked your interest in archaeology?

Prof. Marston: When I was in high school, I had to take a foreign language for the first time. I was not very excited about Spanish or French because they seemed like the typical languages that everyone else would learn. Instead, my school offered Latin, and I thought, “Latin sounds cool. Let’s try that.”

So I started taking Latin, and through that I learned a lot about ancient history by reading this ancient language. I found it really interesting, and I realized that I was more interested in history than I had expected, especially very early history.

As I continued learning, I discovered that there was a field where you could study ancient objects and learn about history from a different perspective. That field was archaeology. I ended up getting an internship at an archaeology museum, where I was able to work with some ancient artifacts. That experience was really exciting, and it made me realize how interesting the field was.

By the time I was getting ready to go to college, I decided that I should attend a school that allowed me to take archaeology classes. However, I originally wanted to be a biologist. I was very interested in the environment and ecology, and that was what I had always intended to study. So I chose a school where I could study biology but also take archaeology classes.

When I started college, I took both archaeology and biology classes. At that point, I learned that there was an area of archaeology that focuses on studying ancient plants. This field combines ecology, botany, and environmental science with the study of history.

When I realized that this field existed, it immediately caught my attention. It brought together all the scientific subjects I was interested in along with the historical side of archaeology. I started taking more classes in that area, and that was the moment when I realized that this was what I wanted to do with my life. I wanted to keep studying this field because it brought together everything I was interested in all at once.

V: That's nice that you found a connection between your two interests.

Prof. Marston: I didn’t know that this connection existed. Then, randomly, I saw this class and thought, “That sounds really cool!”

V: This has been such a fun conversation. Thank you so much for your time.