Mounds at Colina Da Monte
Mounds at Colina Da Monte
Hi everyone! My name is Rocío López, I am a Uruguayan Archaeologist doing my Ph.D. in Anthropology with a specialization in Archaeology at the University of Florida. I’m very excited to share a bit about earth mound archaeology, also known as “cerritos de indios,” in the current territory of Uruguay, in the lowlands of Southeast South America. My research investigates how and why these earth structures were constructed as early as 5000 years ago, and the very long-term relationship between the mounds and the people living in this region.
I have been interested in Archaeology for as long as I can remember. I remember being a 6-year-old girl living in Uruguay and I had my dad always telling me the wonders of past societies in different parts of the world, like the Egyptian pyramids. He brought me “National Geographic” magazines for me to check out all those great stories and pictures. I wasn’t particularly interested in a specific archaeological site, but I was fascinated by three very simple things: people from the past, space, and time. How did people live in the very ancient past? Who were they? And how did people in my part of the world live long ago?
I later realized that those things that fascinated me had to do more with the study of Anthropology and people, than studying “stuff” from the past. I found out that people and things interacted together, talking to each other. The material things, or traces people in the past create or leave behind, not only tell us information about how those past people lived, but material things also shaped those societies into what they were, in a constant loop that went back and forth for a long time. Think of today’s cell phones or laptops for instance. Humans created them, but at the same time, people’s way of communicating and interacting changed forever after we all started using them.
Now, it could be safe to say that I am a Geoarchaeologist. I study how archaeological sites were produced and formed through different geological, geophysical, and archaeological methodologies. One of these types of sites is earth mounds, which is what this kit is all about! Also, when I am not doing archaeology, you will probably find me either running, playing soccer, or at the gym! I really can’t stay still for long.
I hope you enjoy!
Rocío
Anthropology: the study of humans and what makes us human broadly. This is done through different approaches: looking at the past of human groups through material traces and remains; looking at the body, analyzing bones, diet, health, etc.; looking at our relationships, trying to understand how people interact within them, and also looking at languages, and the ways people communicate around the world. (Summarized from AAA website. For more, see: https://www.americananthro.org/index.aspx)
Archaeology: the anthropological study of human cultures through the material remains they made and the material traces they have left behind.
Lowlands: an area of land that is close to sea level or that is lower than most of the land around it.
Material: physical objects that we can perceive using our senses.
Material culture: items people make and use. For example, a wedding dress, a family Bible, and a plastic fork are all examples of material culture. Also sometimes called artifacts.
Geology: the study of the Earth. It looks at how the earth formed, its structure and composition, and the types of processes acting on it. (From The Geological Society website, UK. See more: https://www.geolsoc.org.uk/Geology-Career-Pathways/What-is-Geology)
Geophysics: the study of the subsurface of the earth. It looks at the geology, geological structure, groundwater, contamination, and human artifacts beneath the Earth's surface. (From the Environmental and Engineering Geophysical Society website. For more: https://www.eegs.org/what-is-geophysics--)
Rocío Lopez digging at an earth mound in Colina Da Monte site, Uruguay.
Uruguay is a small country located between Brazil and Argentina, Southeast of South America. It is part of what is known as the “southern cone” of South America. It has a temperate climate and a low grassland landscape. Eastern Uruguay is a very resource-rich area of extensive wetlands that flood seasonally as well as higher lands that remain dry.
Map of South America and Uruguay (Lopez)
In Eastern Uruguay, in many parts of Brazil, and in Eastern Argentina, there are a lot of earth mound structures.
So what are earth mounds? They are elevated soil structures, made by humans, and generally located in wetland and lowland environments. They are made from soils that have been modified by people (burned earth, ash, charcoal, or mixed sediments from diverse places), stone artifacts, animal and plant remains, ceramic pieces, and sometimes human remains.
Earth mounds are a type of archaeological site that can be found all over the world in many different shapes and sizes. They have an immense diversity of shapes and histories, they were created in many different time periods, and people used different methods to build them. There are hardly two alike.
Colina Da Monte picture of Platform Mound (Lopez)
In the lowlands of the East of Uruguay, earth mounds date from as early as 3000 BCE up until the European contact period, around 1500 CE. They can be found isolated, in small groups, or in groups of up to 50 mounds. Large groups of mounds are usually located in higher spots. They remain dry year-round, safe from flooding, but still close to all the wetlands resources. Isolated or small groups of mounds, on the other hand, tend to be located within those resource-rich wetland floodplains. During flooding, the mounds in these very low landscapes would have been surrounded by water. Archeologists in this region have identified more than 1500 mounds, forming what could be called a “mounded landscape”. Within Uruguayan territory, the highest number and size of mound structures are in the India Muerta Wetlands, which covers 384 km2 (~148 sq miles) and contains around 600 mounds!
Colina Da Monte aerial picture, personal drone photo (Lopez)
But where did these earth mounds come from? Did a group of people, or a society, build them on purpose, all at once? Or are they the unintentional result of people living in the same place continuously for hundreds or thousands of years? Could both explanations be true? Can there be another explanation? And how did people use these mounds? What can we tell about the communities that created them?
Decades of archaeological research have reached a general agreement about what happened in this region. Around 5000 years ago (3000 BCE) was a “pre-mound” period in this region. Indigenous groups in the area specialized in hunting and gathering. They moved around a wide lowland landscape on a seasonal basis. They may have rotated from the Atlantic coast of the current Uruguayan territory to the inland wetland areas, to the high hills of Eastern Uruguay. These regions were about 25 km (15 miles) apart. We believe they did this because archaeologists like José Iriarte and José López Mazz have found similar archaeological remains, such as specific types of spear points and similar choices in stones types, on both the Atlantic coast and in the oldest parts of earth mound sites in the interior of the region. The fact that similar remains were found in different places tells us that probably the same people might have been moving around in a wide landscape.
Map from QGIS with Sierra los Ajos mounds and Atlantic coast sites (Lopez)
The environment back then was different from today. It was cooler and drier than now. Since these populations seem to have moved constantly, an archaeologist named Camila Gianotti believes they created “fleeting landscapes”, meaning there is almost no visible trace in the archaeological record of them. They probably did not alter their landscape very much and they did not leave many objects that were preserved until the present day.
After around 2700 BCE, the first isolated mounds or small mound clusters emerge. Archaeologists believe this happened because of the construction of housing units and the effects of people living in the same location generation after generation. Small mound groups appear to be arranged in various forms: circular or elliptical, linear, and “U” forms. In other words, looking down from above, the mounds form a circle/oval, a line, or a U.
José Iriarte believes that during this period there was a rise of household-based communities with a centralized communal space or plaza. He investigated a site consisting of a group of mounds called Los Ajos, located in the Los Ajos hills, where he found many remains of lithic (stone) waste that resulted from making tools such as spear points or stone knives. He also found broken pieces of ceramic from vessels with very simple to no decorations (a typical characteristic of ceramics found in mounds in Uruguay). Moreover, he found remains from different local animals, such as deer, fox, or capybara, and freshwater fishes, as well as microscopic evidence in the soil and in the ceramics of different vegetables such as maize (corn), squash, possibly beans, and Butiá palm nuts. All this evidence tells us that communities here practiced hunting, gathering, and fishing as well as early horticulture involving maize, squash, possibly beans, and Butiá palm nuts.
Colina Da Monte, the site that I am researching, is less than a mile away from Los Ajos, and both have very similar spatial characteristics, meaning the way different kinds of structures were arranged in relation to each other. They each have a large central mound with a flat top (also known as a platform mound) in what looks like a plaza area. The central mounds in Colina Da Monte are made of burned earth and soils from the surrounding area, as well as some stone waste. This plaza area is surrounded by a series of smaller dome-shaped mounds. These outside mounds contain a lot of material evidence of domestic activities, such as food remains, charcoal and burned earth, broken ceramics, and remains of stone tool-making practices.
Archaeologists interpret all this evidence to draw conclusions about the past. According to researchers such as Iriarte and Camila Gianotti, the spatial organization of the mounds in this region suggests that around 2700 BCE, people began to intentionally plan the spaces where they lived and they stopped moving around as much as they had before. Iriarte theorizes that Los Ajos was a village community with a central platform mound for public rituals and outer mounds where people set up their households. The animal, plant, ceramic, and stone remains suggest that these mounds were places where people cooked, ate, and worked on tools. And finally, Los Ajos and Colina Da Monte seem to have been associated villages, since they shared a similar chronology, a spatial closeness, and similar archaeological finds, so they probably knew about each other. Yet, we can't really affirm if they were the same people, if they were different people who traveled between the two sites, or if they shared a culture.
By 1000 BCE these mounds become more common in the region. This coincides with a period when the climate became warmer and more humid. Moreover, according to Gianotti, by this time, some human remains were buried in the plains surrounding earth mounds and therefore outside of these settlements, as well as some occasional burials in mounds, like those found in Los Ajos site. By 1000 BCE mounds were large enough to be seen in the landscape, as monuments within a flat grassland. A person walking through the area would have been able to see these villages from a distance. Researchers believe this period is characterized by a growth in population and so it would have been necessary to generate larger circular villages among the higher wetlands, which began to be occupied more intensively.
Butiá palm trees (Portal Oficial de Turismo Rocha, Uruguayan Government)
Moreover, some researchers, like an archaeologist called Roberto Bracco, believe that earth mound formation has to do with the accumulation of burned soils and trash from earth ovens that people used to process food. He thinks this because most mounds have been found to be made of high amounts of burned earth as well as refuse from daily activities. Burning can also be associated with the intention to increase soil nutrients, disinfect the soil, and get rid of undesirable insects and weeds.
After 1000 BCE there seem to be important changes occurring in the people inhabiting this region. Researchers like José Iriarte, Camila Gianotti, and José Lopez Mazz have spent years investigating several sites in the area. They started to notice evidence of remodeling of previous mounds and the construction of new structures. They believe the people who lived at these sites intentionally prepared the soil to enable them to build mounds that were taller, bigger, and more monumental. This is also when there is greater evidence of old mounds being reused as cemeteries. Why did people use old mounds as burial sites? We don’t know for sure, but maybe it was a way of claiming territory, being more visible, or claiming a connection to people who lived there in the past.
The location of the mounds changed, too. After 1000 BCE there was a decrease in mound construction in the upper highlands and an expansion of mounds towards lower wetlands. Just before the arrival of the first European settlers in the early 1500s, there is evidence in archaeological record of the arrival of Guaraní groups coming from the Amazon. We know this because some mound sites have evidence of Guaraní pottery in their top (most recent) layers. For example, at the Isla Larga site, an archaeologist named Leonel Cabrera and a team of researchers discovered a corrugated ceramic urn with human burials inside it. This type of ceramic pot is very typical of Guaraní groups in this time period. Other mounds in the area have also pieces of Guaraní ceramic remains in their upper (most recent) layers.
Guaraní ceramic urn found at the Isla Larga site (Rocha). Picture modified from López and López 2020.
The earth mound landscape of Uruguay is fascinating to me! The burnt soil, ceramics, plant and animal remains, and other remains allow us to see the changing ways groups of people interacted with these places over thousands of years. This interaction continues in the modern world. Earth mounds are strategic locations with very rich and fertile soils and great visibility of the terrain around them, and so many people today reuse that fertile earth for agriculture or build their houses on them, reusing a space that has been occupied for 5000 years.
Our understanding of the past changes, partly based on new evidence, but also based on our attitudes and biases. What we learn depends on which questions we ask and how we interpret the evidence we find. The narratives about earth mounds in Uruguay are connected to how Uruguay has historically addressed Indigenous populations in general.
Ever since Uruguay’s birth as a country and throughout its history, it has portrayed itself as being the “country without Indians” in South America. In 1831, just after Uruguay became an independent country, the government supported the massive killing of indigenous Charrúa people. There were very few survivors. Then, the early government worked to attract white European immigrants to settle in Uruguay. Together, these events helped strengthen the narrative of Uruguay as “a country without Indians” (“un país sin indios”). This idea was strongly inserted into the country’s historical narrative, being taught in schools and even colleges. Even though some Charrúa people survived the massacres in 1831, they and their descendants often stayed quiet about their Indigenous heritage. If they shared their identity, it was harder for them to get a job and they were very likely to be discriminated against in public settings.
This bias against Uruguay’s Indigenous population also affected researchers. In the 1950s the career of archaeology did not yet exist in Uruguay. In fact, no colleges in Uruguay offered degrees in archaeology until 1986. But in the mid-20th century a different type of scholar, a cultural ecologist named Julian Steward, offered an interpretation about the past Indigenous peoples of the area. He claimed this region was a "marginal area" of South America. In other words, the early inhabitants were simple offshoots from different groups that migrated down from the north. Compared to the Tupi Guaraní to the north and the peoples living in the Andes mountains to the northwest (where the Inka eventually arose), he considered the Indigenous peoples of Uruguay to be simple “marginal tribes”.
A Brazilian archaeologist, Pedro Ignacio Schmitz, also studied the early Indigenous people of the region. In 1976, he interpreted the mounds in Brazil and Uruguay’s coastal lagoon systems as seasonally occupied fishing sites. He theorized that the people who occupied the sites exploited lagoon resources, but also practiced hunting and gathering. In other words, he saw the mounds as the byproduct of fishing practices, not village sites that ancient people created intentionally.
But things have changed in the last few decades. Since 1980, there has been a rise in Uruguayan people claiming their Indigenous heritage. Why did this occur all of a sudden?
Socially, there was a change in the population in Uruguay. In the 1970s and 1980s, a number of Mbya Guaraní families moved to Uruguay. The Mbya Guaraní are an Indigenous group based in neighboring Paraguay. They are related to earlier Guaraní groups who moved into Uruguay’s earth mound region shortly before the arrival of the Europeans. (Of course, back then, the modern borders between Uruguay and Paraguay did not yet exist). These recent Mbya Guaraní families came to Uruguay searching for new spaces to create their way of life. Their arrival, along with the creation of indigenous organizations, helped encourage the descendants of the 1831 survivors of the Charrúa killing to raise their voices and speak out about their indigenous heritage.
Alongside this social change, there has also been a related change in research about the Indigenous past in Uruguay. With the creation of archaeology as a career in Uruguay in the 80s, narratives about the emergence of earth mounds centered on “adaptationist” theories. This is the idea that humans spend their lives adapting to changing environments in order to survive. According to this way of thinking, the environment allows and/or constrains different kinds of cultural practices. Scholars who adopted this point of view saw earth mounds as products of groups that moved through the landscape following resource-rich areas when a dryer climate reduced them in size. From this point of view, the mounds had multiple functionalities, as they could be both living spaces and cemeteries.
Over time, as scholars found different kinds of evidence, this perspective changed. Archaeologists identified traces of crop domestication, water management and intentional construction. Rather than seeing the mounds as – basically – the garbage heaps of hunter-gatherers, archaeologists realized evidence suggested mounds were purposeful creations by people who were modifying their landscape to better suit their way of life. Now they were seen as evidence of social complexity, turning around Steward’s initial idea of this region as a culturally marginal area inhabited by simple groups.
Despite the vast amount of archaeological evidence showing the contrary, the idea of this region being the home for simple marginal groups has persisted. The national and popular narrative is still that before the arrival of Europeans the truly complex societies were in the north and the Andean northwest, that Uruguay was a cultural and social backwater. This is not just because of Steward’s initial interpretation. It is also tied to Uruguay’s emergence as a nation-state. The events of the past few decades challenged the popular notion of Uruguay being the “country without Indians” of South America and there has been a strong denial and backlash from the Uruguayan society and government. A number of diverse actors are in place in this complex net: the Mbya Guaraní groups that arrived in the 80s, the more recently self-acknowledged indigenous Charrúa descendants, the scientific community, and the political voices of the government.
We know today that earth mounds have very long “biographies” as material objects that have been created, modified, and used in different ways by different human groups over almost 5000 years. We know from the archaeological record that prior to the arrival of Europeans, Guaraní people moved into the region and began using some of these earth mounds. This raises questions in modern Uruguay: Are the Mbya Guaraní groups living in Uruguay today “newcomers” into new territory? Or are they part of an ancestral and much larger territory from a time when countries did not exist? How do we understand the identity of an ancient indigenous society that is and was characterized by migration and movement? I won’t try to answer this, since we don’t have an answer for it. I’ll leave you to think on it!
Picture of burned earth found in a Colina Da Monte mound (Lopez)
But what were they burning exactly, and why? Was the burning part of larger and more important activities and practices? Does the burning have something to do with the mounds being formed and lasting thousands of years?
Let’s talk about physics for a moment. Soil is made of different-sized pieces of rocks: gravel, sand, clay, and silt, plus water, and other chemical components. Now imagine making a fire in a fire-pit when you go camping. The soil underneath the fire will be heated at high temperatures, and one important effect of this is that the microscopic water particles that exist in the clayey part of the soil will evaporate and disappear. This turns the soil under the fire-pit into dryer, more compact, more solid, and less porous earth. Now imagine doing this repeatedly for thousands of years in the same place. This would produce an elevated mound that lasts for a long time. Because the mound contained a lot of burned earth, natural processes would not erode the mounds. They would last instead of being erased them from the landscape.
Some archaeologists, like Laura Del Puerto, suggest that the fire that created the burned earth in Uruguayan mounds was mostly associated with past people’s everyday activities. For example, her interpretation of the evidence is that they used fire for cleaning domestic spaces, cooking, heating stone (as part of the process of making stone tools), producing ceramics, and burning waste. This is because those patches of burned earth have been found alongside other remains such as animal bones, ceramics, and stone artifacts in a mound site called La Tapera. Other archaeologists, like Roberto Bracco, claim that the burned earth in the mounds is because people built prehistoric ovens for food processing. His interpretation is based on chemical evidence in the soil at a mound site called García Ricci.
Regardless of the reason for these fire practices, it is undeniable that they had a significant role in the formation and permanency of the mounds we see today in the Uruguayan landscape.
As you can see in the picture, mounds are generally very visible in the landscape. Partly, this is because they look like hills in the middle of flat terrain. Some are up to almost 7 meters (23 feet) tall, and up to 35 meters (115 feet) in diameter. But also, because they usually have different vegetation on their top that contrast with the surrounding grasslands. These are called “forest islands”.
Picture of mounds at Colina Da Monte (Lopez)
These forest islands are a great way to identify earth mounds in the field today and are also an ancestral trace of the human impact in the landscape, caused by thousands of years of human activities in the same place. These are forest islands growing on top of mounds grow grasses, plants, herbs, and forests that are different than those outside the mound. These are highly valued by local people today for their uses, such as edible, medicinal, construction, technological, and environmental uses.
These kinds of vegetation grow on the mounds but not in the grasslands around the mounds because different plants do well in different kinds of soils, and the earth in the mounds is different compared to the earth around them. The earth of the mounds is not natural soil. It is called “anthropogenic” soil because it has been changed a lot by human activity, or even in some cases intentionally produced to make a mound. This is why the vegetation that grows in the mound looks different than the vegetation that grows in the natural soil around them.
Many researchers all over the world, such as William Baleé and Clark Erikson in the Bolivian Llanos de Mojos area, and Roberto Bracco and Laura del Puerto in the Uruguay lowlands, have investigated this vegetation and soil difference. They analyzed the specific and unique soil properties inside the mounds, as compared to the soil properties of the natural soil around the mounds. They noticed that the earth in the mounds had extremely high levels of some chemical elements like phosphorous, potassium, as well as organic matter, in comparison to those same elements in the soil around them. This indicates very high levels of human activity for a long time.
At the same time, these researchers showed that mounds have permanently affected the distribution and movement of the animal and plant species within mounded landscapes. A comparison of the biodiversity found in the mounds and the biodiversity found in the rest of the landscape led to the conclusion that the mounds’ forest islands have far richer biodiversity than the rest of the landscape. Archaeologists in different parts of North and South America have noticed this is a common feature of mounds in many different places.
So how does this relate to climate change? Climate change is causing a loss of biodiversity and degrading ecosystems – the exact opposite of forest islands on the mounds. By studying mounds, like the ones in Uruguay, researchers can help humanity today to come up with sustainable conservation strategies and ways to fight the loss of biodiversity and ecological degradation. By understanding practices from the past, we might be able to improve our present world.
Earlier I mentioned that there are many kinds of mounds around the world. For example, there is another kind of prehistoric construction, found in many locations all over the world and very similar in shape and size to earth mounds. But instead of being made out of earth, these other mounds are made mostly of shells. In the East of South America, these are often called shell mounds or middens. In Brazil, where they are very common, they are called “sambaquíes”. There, they were built in resource-rich spots near the coast.
Aerial view of Monte Castelo shell mound, Brazil. (Courtesy of Pugliese et al. 2018)
According to research done by a Brazilian archaeologist named Paulo De Blasis and other collaborators, the first shellmounds appear around 8000 years ago (6000 BCE) as funeral monuments near the Atlantic coast and in lagoon environments. Evidence suggests they were almost permanently occupied for thousands of years, until the arrival of the first Europeans in the early 1500s. They are usually made of layers of earth, sand, and shell. Within the layers, researchers have found the remains of shells, fish, fishing tools, charcoal, burned animal bones, hearths, and human burials. This evidence suggests that shellmound-builders got their food from fishing, as well as hunting and gathering. Some researchers, like Brazilian archaeologist Daniela Klokler see these remains as evidence of funeral feasting celebrations among the communities. Others believe that they might have been campsites or processing food stations when human burials are not found in them.
Together, earth mounds and shell mounds cover a vast almost continuous region in the Southeast of South America and given their similar forms in the landscape it is possible to make some comparisons. The earliest evidence of shellmound construction goes back to 8000 years ago (6000 BCE) and the earliest evidence of earth mounds in the region dates back to almost 5000 years ago (3000 BCE), in the India Muerta Wetlands of Uruguay. So, the earliest shellmounds were built before the earliest earth mounds. However, the vast majority of the shellmounds in what is now Brazil were erected between 5000 and 2000 years ago, right at the same time when earth mounds were emerging in Uruguay. Also around 5000 years ago, shellmound-builders began practicing forest horticulture. They combined this with fishing, hunting, and gathering, according to archaeologists Suzanne and Paul Fish. This means they adopted horticulture just a little earlier than the earth mound-builders farther south.
It is not possible to say that earth mounds and shell mounds are the constructions of the same population, given their spatial, chronological, and archaeological differences. Nevertheless, it seems that 5000 years ago societies in this part of the world were going through a key moment of change. Shellmounds began an explosive construction period around the same time earth mounds started to appear. As monumental constructions, shell and earth mounds both became highly visible, permanent ancestral traces in the landscape of the South American continent.
"The Prehistoric Mounds of Uruguay: linking the past and the future" from The Archaeology Channel
"The genomic prehistory of the Indigenous peoples of Uruguay" from PNAS Nexus