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Those Sophisticated Cave Men--Earthmovers of the Amazon: & An Artificial Landscape-Scale Fishery in the Bolivian Amazon --Page 23

by Charles C. Mann

"Are the mounds, causeways, and canals in Bolivia’s Beni region natural formations or the result of 2000 years’ labor by lost societies?"

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TRINIDAD, BOLIVIA—In some ways, William Denevan says today, he didn’t know what he was getting into when he decided to write his Ph.D. thesis about the Beni, a remote, nearly uninhabited, and almost roadless department in the Bolivian Amazon.

Located between the Andes Mountains and the river Guaporé (a major Amazon tributary), the Beni spends half the year parched in near-desert conditions and the other half flooded by rain and snowmelt.

But it wasn’t until he made his first research trip there, in 1961, that Denevan realized the area was filled with earthworks that oil company geologists—the only scientists in the are—believed to be ruins of an unknown civilization.

Convincing a bush pilot to give him a flying tour, Denevan examined the earthworks from above. Much of the Beni is covered by a savanna known as the Llanos de Mojos (the Mojos Plains). But, to his amazement, Denevan saw what seemed to be the remains of transportation canals, pyramid-like mounds, elevated causeways, raised agricultural fields, and clusters of odd, zigzagging ridges scattered through the savanna.

“I’m looking out of one of these DC-3 windows, and I’m going berserk in this little airplane,” recalls Denevan, who is now a professor emeritus of geography at the University of Wisconsin, Madison. “I knew these things were not natural. You just don’t have that kind of straight line in nature.”

fish weir



The discovery of over 500 square kilometers of artificial earthworks that are identified as fish weirs by a team of American and Bolivian archaeologists directed by Dr. Clark L. Erickson of the University of Pennsylvania Museum of Archaeology and Anthropology.


Baures, located in the eastern tropical lowlands of Bolivia, South America. The region, known as the Llanos de Mojos, is characterized by savannas, wetlands, and tropical forest.


The native peoples, the Baures, built a vast network of fish weirs, ponds, canals, and causeways to harvest fish and other aquatic resources.


The availability of protein is considered by some scholars to be a “limiting factor” in settlement and cultural development in the Amazon region. The Baure solved this problem by transforming the landscape into a large artificial fishery. They could efficiently harvest and manage aquatic resources using indigenous technology. The Baure were able to sustain large populations on the savanna.


The earthwork complex was probably built and used in late prehistory and during the early colonial period (around AD 1600-1700).

Why is this important?

The Baure fish weirs are a remarkable example of indigenous knowledge and technology. We can learn valuable information about sustainable land use from this past culture that may have applications in the contemporary world.

The publication in the journal Nature [November 7, 2000] "An Artificial Landscape-Scale Fishery in the Bolivian Amazon" presents new archaeological research on massive anthropogenic transformation of the landscape in Amazonia.

The manuscript documents how Native Americans of late prehistory transformed a marginal environment into a productive landscape capable of supporting large and dense populations.

Archaeological fieldwork included survey, mapping and excavation of fish weirs and related infrastructure in the Bolivian Amazon.

Based on form, patterning, environmental context, and ethnographic analogy, the earthworks are identified as fish weirs. There are no documented artificial fisheries of this scale, permanence, and sophistication in the published literature on Native Americans.

The hydraulic complex represents a grand accomplishment of landscape engineering and environmental transformation by Amazonian peoples.

The research shows the contribution of archaeology and historical ecology to understanding the present environment of the Amazon and how it came to be. This case study is relevant to environmental studies, ecology, conservation, freshwater fisheries, wetland studies, anthropology, geography, and Latin American Studies.

The research has implications for applied studies of sustainable development, conservation of biodiversity, and indigenous knowledge systems.

Francisco de Orellana Testified To Advanced State & Dense Number of Amazonians

Francisco de Orellana, one of the original Conquistadors, was in charge of the first European expedition down the Amazon river. His story is remarkable not least because it was a completely accidental voyage of discovery.

He and 60 men had been separated from another expedition led by Gonzalo Pizarro who had been in search of cinnamon in the jungles of Ecuador. Their boat had been carried downstream by the swift current of the Napo river which turned out to be a major tributary of the Amazon.

Seven months later their boat arrived at the Atlantic coast, more than 6,000 kilometres away from where they started out.

Orellana and most of his crew managed to make it back to safety and they brought with them fantasic tales of the sights they had seen on this river. Orellana described the Amazon as a busy waterway which had on both sides of the river populous towns with elaborate temples, plazas and fortresses. As his chronicler, Fray Gaspar de Carvajal relates it:

...we tarried so long in this land of Machiparo's which is 80 leagues in extent, all speaking one language and densely populated with towns and villages with scarcely more than a crossbow shot between them. Some of the towns extended for five leagues without any separation between the houses, quite a wonderful thing to see [a league is about 5.5 kilometres].

The people they encountered lived in towns and villages along the river and were organised into confederations which traded and fought with another. As Orellana's party moved downstream from the Napo to the Amazon proper they found the region becoming more populous, and at this confluence there were great numbers of people and a very pretty and a very fruitful country.

Being already the lands and mountains of the Omagua and having so many large towns with so many people who did not like us to land in their port, we had to fight our way through.

The river communities were well connected and the expedition faced increasingly stronger opposition as they passed through more and more territory hostile to their presence. Orellana's group had little in the way of weaponry and knew how important it was to conserve the little gunpowder that they had so they tried to avoid fighting the Indians as much as they could.

That said, however they were after all conquistadors and they survived by plundering the villages of their food stocks and they committed several atrocities along the way including burning down a dwellings with women and children inside.

This could not have helped but enrage the local population. In some places they had to ward off attacks by armies of Indians several thousand strong.

There was great amount of food, that turtles in corrals and alberques of water, and much meat and fish and sponge cake, and this in as much abundance that it could have fed a army of a thousand men for a year which we took from this population without resistance. We also found much food in the way of a special fish that was so much in abundance that we could load well our brigs. This fish the Indians take up into the mountains to sell.

The Omagua people also produced arts and crafts of a very high level. Carvajal describes their pottery: ...there was a villa in which there was a great deal of porcelain ware of various makes, both jars and pitchers, very large, with a capacity of more than twenty-five arrobas, and other small pieces such as plates and bowls and candelabra of this porcelain of the best that has ever been seen in the world, for that of Malaga is not its equal, because it is all glazed and embellished with colours, and so bright that they astonish, and, more than this, the drawings and paintings which they make on them are very accurately drawn just as with the Romans.

None of the tricks that had served the Europeans so well when dealing native peoples seemed to work. When they attempted to trade useless trinkets for gold, the Omagua valued what the Spaniards offered for exactly what they were worth:

...a canoe came up to the gourd containing the chaqutra, and they picked it up and showed it to the other Indians, and they valued it so little that it became evident to us that they were making fun of it.

Even a brief account of Orellana's expedition would not be complete without mentioning their encounter with an army of natives taht fought under the command of female warriors. The classically inclined Spaniards naturally named these women "Amazons".

...we came suddenly upon the excellent land and dominion of the Amazons. These said villages had been forewarned and knew of our coming, in consequence whereof they came out on the water to meet us, in no friendly mood. ...Orellana gave orders to shoot at them with the crossbows and arquebuses, so that they might reflect and become aware that we had wherewith to assail them.

The Spaniards continued on but had not gone more than half a league before they encountered and were forced to do battle with several squadrons of Indians led by ten or twelve Amazons who fought in front of all the Indian men as women captains, and these latter fought so courageously that the Indian men did not dare to turn their backs, and anyone who did turn his back they killed with clubs right there before us.

[these women were] very white and tall, and have hair very long and braided and wound about the head, and they are very robust and go about naked, with their privy parts covered, with their bows and arrows in their hands.

It was only after seven or eight of the women were killed that "the Indians lost heart, and they were defeated and routed with considerable damage to their persons." Although Orellana had wished to name the great river after himself, it was the more evocative name Rio del Amazonas that is the one we know today.

So the question that has been asked ever since is: Were Orellana and Carvajal lying when they said that the Amazon basin was heavily populated and urbanised? The seemingly objective style and the great attention to minor details in the narrative does make this somewhat hard to believe.

Presumably some things were exaggerated but Carvajal's geographic and linguistic descriptions have since proven to have been accurate.

The problem is that there are little in the way of documented accounts of contact with the Omagua for a century after this and information about the region remains scanty until the end of the 18th century. By this time the Omagua and their towns had long since vanished almost without a trace. ....."

Today, almost 4 decades later, a small but growing number of researchers believe that the Beni once housed what Clark L. Erickson of the University of Pennsylvania, Philadelphia, calls “some of the densest populations and the most elaborate cultures in the Amazon”—cultures fully as sophisticated as the better known, though radically different, cultures of the Aztecs, Incas, and Mayas.

Although these still unnamed peoples abandoned their earthworks between 1400 and 1700 A.D., Erickson says, they permanently transformed regional ecosystems, creating “a richly patterned and humanized landscape” that is “one of the most remarkable human achievements on the continent.”

To this day, according to William Balée, an anthropologist at Tulane University in New Orleans, the lush tropical forests interspersed with the savanna are in considerable measure anthropogenic, or created by human beings—a notion with dramatic implications for conservation.

These views have thrust the Beni into what Denevan calls “the Amazon archaeology wars.” For more than 30 years, archaeologists have clashed, sometimes in bitingly personal terms, over whether the vast river basin could provide the resources for indigenous cultures to grow beyond small, autonomous villages. Until relatively recently, the naysayers had the upper hand.

In the last decade, though, several archaeologists, including Anna C. Roosevelt of Chicago’s Field Museum, have published evidence that such societies did exist throughout the várzea, as the Amazonian floodplain is known, and the bluffs above it (Science, 19 April 1996, pp. 346 and 373; 13 December 1996, p. 1821).

The dispute over the Beni is similar. Using environmental arguments, skeptics contend that the Beni earthworks must be either natural formations or the remains of a short-lived colony from a richer part of South America—the Andes, most likely.

“I haven’t seen any basis for thinking there were large, permanent settlements there,” says archaeologist Betty J. Meggers of the Smithsonian Institution in Washington, D.C.

“But if they were there, where is the solid evidence?” In particular, critics like Meggers point out, there is no indication of hierarchical organization in the Beni. Without it, they say, the kind of sophisticated society envisioned by Denevan, Erickson, and Balée could not have existed.

Resolving the controversy may have important consequences for the region—and all of Amazonia. If the region is inherently too fragile to support intensive use, its most appropriate future may be as a biosphere reserve supervised by the United Nations Educational, Scientific, and Cultural Organization (UNESCO)—that is, as an almost uninhabited eco-park.

But if human activity has played an essential role in the region’s ecological processes for millennia, as Balée argues, then careful human exploitation of the land—such as allowing indigenous people to till land in areas used by ancients—is not only acceptable but essential to preserving its character.

“Without a doubt the Llanos de Mojos represents one of the most extraordinary prehistoric landscapes anywhere on the face of the planet,” says Robert Langstroth, a cultural geographer who did his 1996 PhD. dissertation at the University of Wisconsin under Denevan. “The question is, how much of it is archaeological, and how much did the archaeological parts affect the natural?”

Anthropological El Dorado

For centuries, the Llanos de Mojos guarded its story well. A shelf of alluvial deposits as much as 3000 meters deep, the savanna was once rumored to house the golden city of El Dorado.

Protected by its clouds of insects, its climactic extremes, and its inhabitants’ reputation for fierceness, it was among the last areas in South America reached by Europeans.

In 1617, a ragtag band of explorers finally established that El Dorado did not, in fact, exist in the Llanos de Mojos. The Jesuits ruled the area from 1668 to 1767, while disease ravaged the indigenous people.

Even after the destruction wrought by the Spaniards, the Beni hosted a remarkable mosaic of indigenous societies until the mid-20th century. Its cultural diversity—and the relative lack of knowledge of the area— led the Smithsonian anthropologist Alfred Metraux to call eastern Bolivia "the El Dorado of anthropologists" in 1942.

"Some of the Indians came in touch with the Spaniards during the First years of the conquest; [but] others even maintain their independence today and are among the few natives of South America who still live as they did before the arrival of the whites."

Despite Metraux's enthusiasm—and the impetus provided by Denevan's later work on the earthworks—the Beni remained largely unexamined. U.S. researchers were put off by Bolivian political instability, by the difficult climate of the area, and by anti-American sentiments fueled by the heavyhanded presence of the U.S. Drug Enforcement Agency in the region.

For their part, Bolivian archaeologists focused on the highland civilizations of the Andes, with their enormous, glamorous stone ruins. Only in the 1990s did a Bolivian-American team led by Erickson begin the first long-term archaeological research on the earthworks of the area.

Cultural Mosaic

Climbing to the top of Ibibaté, a forested loma (mound) 18 meters higher than the surrounding savanna, Erickson comes to a bare patch of earth created by a fallen tree. Bending over the uncovered ground, he points out the dark, almost black soil, which is filled with fragments of pottery.

Several pieces of pot rim are visible, along with the leg of a vessel shaped like a human foot. Both the richness of the soil and the abundance of the potsherds are typical, in Erickson's view.

"Many of the lomas are almost nothing but enormous heaps of sherds," he says. "I've never seen anything like it—10, 20, 30 feet of sherds"

Ibibaté—"big mound" in the language of the local Sirionó Indians—is about 50 kilometers east of Trinidad, the provincial capital. The focus of ongoing study by Balée, Erickson, and a team of Bolivian scientists working with Erickson, Ibibaté is actually a pair of mounds connected by a short earthen wall.

At the edge of the lower, southern mound is a Sirionó hunting camp; the higher mound is used for gathering fruit and nuts. Several earthen causeways radiate out like highways from the mound toward other mounds.

Bordered by narrow canals, the causeways are about a meter tall, 3 to 5 meters wide, and straight as a rifle shot. Such features are rare in floodplains, according to Denevan, which to him suggested an artificial origin.

Indeed, in Balée's opinion, Ibibaté is "as close to a Mayan pyramid as you'll see in South America. ... Beneath the forest cover is a 60-foot [18-meter], human-made artifact."

Although their research is incomplete and mostly still unpublished, Erickson and Balée have sketched out a rough outline of what they believe happened here. Ibibaté, like most of the hundreds of lomas in the Llanos de Mojos, was initially a much smaller mound, if it existed at all.

It was built up, Erickson says, by the original inhabitants of the Beni, although how and why remain uncertain. They could have begun by raising parcels of land to grow crops above the floodwater.

Or, according to the late petroleum geologist and amateur archaeologist Kenneth Lee, they may have created the mounds when, for religious reasons, they buried their ancestors in ceramic urns and set up housekeeping on top of them.

In either case, the people raised the lomas further by accumulating, garbage, the walls and roofs of collapsed wattle-and-daub houses, and, especially, smashed pottery. "The quantity and mass of material deposited indicates that a lot of people were responsible, creating the mounds over a period of at least 2000 years," Erickson says, "hazarding a guess" that Ibibaté typically housed 500 to 1000 inhabitants.

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Life in the Llanos. An artist’s conception of a settlement in the Llanos de Mojos, some 2 millennia ago. (painting by Dan Brinkmeier)

The villages, each on its own island of higher ground, were anything but isolated. By studying the geographic distribution and variety of the earthworks and their associated pottery, Erickson's team has tentatively concluded that the Llanos de Mojos was the home of not just one pre-Columbian people but a complex mosaic of societies linked by networks of communication, trade, alliance, and probably warfare.

Beginning 3000 to 5000 years ago, Erickson has written, these cultures erected "thousands of linear kilometers of artificial earthen causeways and canals, ... large urban settlements, and intensive farming systems."

For reasons that are still not completely understood, the whole social network unraveled about the time of Columbus or soon after.

Smallpox may well have visited the area—many researchers think that an epidemic of the disease greatly weakened the nearby Incan empire in about 1525. In addition, Meggers believes that the Beni, like the rest of Amazonia, was subject to catastrophic droughts.

Erickson's team and local farmers erected their own raised fields to see how they might have worked. They concluded that the original inhabitants of the Beni probably employed traditional agriculture, growing beans, squash, sweet potatoes, and manioc on raised fields; agroforestry, planting groves of palm, nut, and fruit trees; and—perhaps surprisingly—aquaculture.

Around the causeways in a northeastern region of the Beni known as Baures, Erickson says, run long, low, zigzag earthen walls that stretch for as much as 3 to 4 kilometers.

The structures, he believes, were fish weirs, used when the rainy season covered the savanna with up to half a meter of standing water. Narrow channels up to 3 meters long open at angles in the zigzag. There, woven nets could be used to harvest fish and shellfish, Erickson says.

The openings also funneled fish into artificial ponds as much as 30 meters across. In addition, the weirs are piled high with shells from apple snails (the edible gastropod genus Pomacea), possibly discarded after meals.

The structures persist, although no one maintains them any longer; even today, the ponds pullulate with fish during the dry season.

"They converted the savanna into huge fish farms," says Erickson. "When you see the weirs radiating out from the causeways, I don't think there's any doubt of the intentionality."

Archaeology Wars

Others strongly disagree, in terms that mirror archaeology's long-standing disputes about Amazonia. In influential books and articles, Meggers and her husband, the late Clifford Evans, argued that despite its rich flora, the river basin's thin, acidic soils can't hold enough nutrients to permit sustained, intensive agriculture.

And that means big, complex societies—which inevitably depend on agriculture—cannot long exist in Amazonia. Indeed, Meggers once proposed that Amazonian villages could contain no more than 1000 inhabitants before collapsing. "We call these cultures 'primitive,' ' she says of contemporary indigenous groups, which are some of the least technologically advanced in the world. "But they are actually remarkable accommodations to severe environmental limits. They show us what's possible there."

When researchers claim that large, complex societies existed in Amazonia, she says, it shows only that "there's a lot of tricky environmental stuff that most archaeologists either ignore or don't know about." Because tropical lands are washed by frequent, heavy rains, she says, the traces of human occupation are flushed through the soil rather than being deposited in neat layers.

Thus a place that was intermittently occupied by a few people can seem to have been settled permanently for long periods—the layers are smeared out. "The climate hides evidence of disoccupation," she says. "The charcoal samples get displaced. There's a whole list of pitfalls and problems."

Click and drag photo to resize. In the early 1980s, Bernard Dougherty and Horacio Calandra, two Argentine archaeologists backed by the Smithsonian, excavated several Beni lomas similar to Ibibaté, though smaller. They concluded that the mounds were "not difficult to ascribe" to natural forces, especially "fluvial activity."

In their view, the causeways and raised fields of the Llanos de Mojos were probably created by a higher culture, perhaps from the Andes, which set up short-lived colonies that winked out under ecological pressure.

“It seems that here, as in other parts of the world, the environment had the winning ace from the beginning. Calandra and Dougherty wrote in 1984. In his dissertation, Langstroth argued, in parallel, that the isolated forests were not created by humans.

“They were created by fragmentation and erosion of natural levees," he says. “It sounds nice to give people credit for doing wonderful things, but the evidence isn't there."

Erickson's critics have also pointed out that structures like lomas, causeways, and raised fields require sustained mass labor, which in turn requires the coercive, centralized authority and hierarchical division of labor characteristic of state-level societies. Yet in lowland Amazonia, as Erickson concedes, there is "no good historic or ethnographic evidence" for such vertically organized states.

Erickson has a different explanation: The earthworks, he suggests, were erected by "heterarchical" societies: groups of communities, loosely bound by shifting horizontal links through kinship, alliances, and informal associations.

"There are some people working in South America who take a look at massive complexes of raised fields and say. This has to be organized by a complex polity,' " reports Peter Stahl, an anthropologist at the State University of New York, Binghamton. "Whereas Clark [Erickson] says, 'No, this is the accumulated landscape capital of generations of farmers who built it more or less on their own.' "

Like Erickson, Roosevelt believes that sophisticated pre-Hispanic cultures occupied the middle and lower Amazon areas she has studied. With abundant fruit, nuts, edible palm, and fish, she says, river-basin peoples "had lots of options that people in [less naturally rich] places like central Mexico didn't have— they could always run away and do what they wanted."

The result, in her view, was "much less coercive" societies—“more like epic chiefdoms, where the leaders sponsor buildings and ceremonies"—somewhat like the wealthy, relatively relaxed Indian cultures in the Pacific Northwest and California. “And we're still learning," she says, “about how they shaped this wonderful landscape they bequeathed us."

Researchers who deny the importance of the pre-Hispanic Beni cultures, Erickson explains, have been misled by “archaeology's traditional Fixation on individual sites." The traditional method of digging individual sites and measuring their contents is unlikely to produce clear data, Erickson says, for the very reasons Meggers cites: The area's heavy rainfall mixes up sedimentary layers, and the local practice of heaping up earth to create mounds and causeways farther jumbles the archaeological record.

So, he argues, traditional site excavation must give way to a study of the landscape as a whole—“treating the landscape like an artifact, as if it were a piece of pottery." Such “landscape archaeology" uses nontraditional tools, including aerial photography, radar imagery, and multispectral satellite imagery, to prepare digital maps of large areas.

"My main critique of the site concept is that it implicitly puts edges around each site. But here in the Beni, the 'sites' go on forever--the whole landscape has been organized and designed."

A flight in a small plane over the area makes Erickson's meaning clear. “This group of islands is connected with that one, but not those," he says, shouting over the noise of the propellers. “There's a relationship there. -. The raised fields are all aligned in a north-south direction. The landscape is telling us something."

Ecological adaptation

Erickson and others argue that the Beni mound builders began a process of ecological change in the region that continues to this day. Balée, for example, says the Beni, in his view, was “not favorable for well-drained tropical forests until after people— deliberately or not—made it favorable for them" by raising the mounds above the floodwaters and enriching the soils by burning, mulching, and depositing wastes.

After the original inhabitants of the lomas disappeared 300 to 600 years ago, the mounds were presumably colonized by forest.

When the Sirionó arrived on the scene—Balée believes, on linguistic evidence, that they emigrated to the Beni about 3 centuries ago, probably from the south—they altered the composition of these forests to suit themselves, creating what Balée calls “artifactual forests."

As evidence, Balée points to one of the most common tree genera on the loma: Sorocea, which is used by the Sirionó to make beer. In the Beni, Sorocea is found only on the mounds, not in the surrounding land with standing water, which to Balée is "strong evidence" that people brought it to the lomas.

Similarly, the spiny palm (Astrocaryum murumuru), which has many indigenous uses, is much more common on the lomas than elsewhere—“there's 112 of these here," Balée says at Ibibaté, “as opposed to something like 15" in an equivalent nonmound area.

“There is more forest in the Llanos de Mojos because of people in pre-Hispanic times than in spite of them," Balée says. To him, this indicates "that there is no necessary incompatibility between human use and biodiversity in the tropics," and he hopes that conservationists, who sometimes view human actions as a priori destructive, will not seek to curtail the Indians' freedom.

Active efforts are being made to protect the Beni and its remaining indigenous peoples from over-development. After some hesitation, the Bolivian government has established more than a dozen reservation-like areas for Indian groups, although in some cases they provide little actual protection. Partially overlapping the indigenous areas for the Baures and ltonama peoples—the two easternmost reserves—is a proposed Kenneth Lee Scientific Reserve, named after the U.S. petroleum geologist whose vigorous advocacy of the Beni inspired many researchers, Erickson among them. (Lee died in 1997.)

The Centro de Investigación y Documentación para el Desarrollo del Beni, a Trinidad-based nonprofit organization that seeks to develop the area in ways that would benefit indigenous groups, favors the plan.

Meanwhile, some environmental groups would like UNESCO to create a World Heritage Site in the eastern Beni. There are already three such reserves in Bolivia, though none in the Llanos de Mojos. Presumably, the first priority in such a management scheme would be conservation—a stance that worries Denevan.

“The Indians created the environment we're trying to protect," he says. “They should get to stay there while we're learning what they did."

Original Source: 4 February 200 Vol287:786-789 SCIENCE

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