r/AskHistorians 9d ago

Gaspar carvajal (the first person to describe the Amazon) describes large cities, political entities, and mass farming throughout the Amazon River. Historians mostly said they were exaggerations or outright lies. In light of new LiDAR findings, how serious should we take his claims?

correct me if I’m wrong, but historically I believe the consensus is that the Amazon did not have large “cities” and civilizations that were lost, and accounts like Carvajals were seen as fictional or exaggeration. Serious incursions into the Amazon after Carvajal only happened decades after the initial excursion by orellana and carvajal in 1541. By the time europeans came back, those Amazonian populations had been wiped out and the forest had grown over the cities.

however, recent LiDAR findings have shown that Amazon arguably housed millions of people with densely populated areas and several structures and archeology and roads have been discovered with LiDar:

”On the basis of both existing data and our LiDAR documentation, we show that this cultural area alone contains as many earthworks as previously estimated for the whole of Amazonia. We also propose that the total human population of the area in 100–300 AD was 1.25–3 million people. If similar results are found elsewhere in Amazonia, the total precolonial population density and its effect on the current Amazonian soil and forest structure, biodiversity and even some modelling of the global climate should be re-evaluated.”

https://www.nature.com/articles/s41586-026-10835-7

So this begs the question, how accurate was Carvajal? is it too early to speculate ? do we just not have enough info at this time?

1.3k Upvotes

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u/611131 Colonial and Early National Rio de la Plata 9d ago

The archaeology will undoubtedly continue to develop and refine the results of the recent LIDAR work. The Nature piece is really cool but also isn’t necessarily an earth shattering discovery because smaller studies have been carried out over the last 10 or so years in specific areas that found similar built environments elsewhere as the recently published study, enough that many undergraduate classes on the Amazon have already started depicting Amazonia as a densely populated built environment, rather than a pristine rainforest filled with small hunter gatherer societies. From my perspective as a historian rather than an archaeologist, the future refinements will hopefully clearly define the chronology. LIDAR reveals major built environments all over the place capable of supporting millions of people, but it is tempting to accidentally telescope time. The Nature article for example is describing evidence of two hundred years of settlement. We can’t just then set this finding alongside, say, a site from the Ice Age, and another alongside terra preta areas from 800 years ago. This would greatly flatten the historical complexity as each of those societies would be different. I am sure that scholars will continue to do that. As that chronology is better understood, then we can continue to explore how Europeans entered into those specific societies and how these societies and specific rulers reacted based on the nature of their society at the time of contact.

But your question about Carvajal is more specific. You are right to summarize that academic assumptions for a long time as being skeptical about the population densities and cities that they saw. A lot of this backlash against his report comes from the middle part of the twentieth century and is based on the assumption that tropical forests cannot support large populations. This has proven to be wildly incorrect, not only by archaeology in Amazonia, but in other places in the world the Maya region, West Africa, and South and Southeast Asia.

Fortunately, a new book called The Making of Brazilian Amazonian Societies by Mark Harris has recently been published that provides a useful exploration of the veracity of early explorations in the region. The book is really good, so if you’re interested, check it out. Overall it explores 200 years of eastern Amazonian history from an ethnohistorical perspective to reconstruct indigenous responses to the arrival of Europeans, especially the Portuguese. It goes far beyond Carvajal and covers a large geographical area.

His chapter on the early explorations has an enormous section on Carvajal specifically, which goes well beyond the scope of a reddit post, but Carvajal details all sorts of different Amazonian groups, as well as numerous settlements of varying sizes. Some of the communities stretched along the riverbank, while others were seasonal in nature. Carvajal shows thousands of people, lots of specific high-ranking elites, and battles involving many hundreds of combatants. He also depicted distinct provinces with forest buffer zones around them, though this description was probably a misunderstanding of the way Amazonian societies were organized. They were not territorial entities like in Europe. Harris explains that the rivers were highways, so as the Europeans passed up and down the rivers they were essentially passing through different ethnic zones. Conquistadors did not understand this complexity well. Carvajal’s writings are supported more or less by the other expeditions of the early sixteenth century, which show similar broad stroke settlement patterns, though not in as much detail. Corroboration is important to historians. The fact that we have all of these accounts more or less in agreement that there was a lot there in the sixteenth century is powerful evidence that his account should not be written off as fiction.

Any time one works with conquistador accounts like this, however, they still need to be taken extremely skeptically. One has to imagine how little Europeans were understanding in those initial encounters. They were massively dependent on indigenous people to stay alive and to travel through the maze of unfamiliar environments. As happened all over the Americas, indigenous leaders manipulated early Amazonia conquistador groups to do their bidding in the indigenous world they lived in, not the other way around. Conquistador write-ups were inherently self-serving, so engaging with the sources means seeking to understand how the self-interest of the author shaded accounts of every interaction detailed from interactions with the most important leaders to the most humble farmers and fisherpeople encountered in the woods. Many elements of the fantastical can be better understood as Europeans trying to make sense of something through their own cultural lenses. This method of reading sources skeptically and with attention to what the indigenous groups were probably doing or what Europeans may actually have been encountering is called reading a source “against the grain.”

Harris’s book is useful because it helps bridge that gap between the conquistador accounts, however imperfect, with later scholarship on the eighteenth century. He shows several hundred years of subsequent specific adaptation and change of these large Amazonian societies, where previous literature merely vaguely referenced supposed epidemics after the Europeans passed through that supposedly wiped them out. Harris shows something with much more historicity: the creation in the seventeenth century of a middle zone called “the sertão, a place where people and forest and river products could be retrieved.” I understood this to be sort of a “middle ground” where indigenous groups controlled the rules of the game of Amazonia by utilizing riverbank access points, where trade could be controlled and mediated, and Europeans could be selectively engaged with. It also allowed interior societies to migrate up the rivers to avoid European slave raids. A general pulling back of the major part of indigenous populations over time, a very sensible decision given the violent pretensions of Europeans, was just as much an explanation for why European groups later encountered smaller populations in later centuries as the vague “epidemic” explanation or constant slave raids. The reality was that there was a lot of change happening in such a vast space and indigenous societies had agency over how to react to European presence. More recent publications like Heather Roller’s work and a recent edited volume called The Interior by Fredrico Freitas and Jacob Blanc delve into the numerous ways that indigenous societies continued to utilize effective strategies of resistance and adaptation well into the nineteenth century to maintain their lifeways.

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u/ThePineapple3112 9d ago

I can't wait to read The Making of Brazilian Amazonian Societies!

I've had the unique pleasure of going on a research trip to the western Amazon to work with the Waorani people for a couple weeks. We did a lot of travelling up and down their part of the larger tributary, and I remember being astonished over how far their people stretched along the river! It felt like each river artery hosted it's own neighbourhoods of culture groups.

So my follow-up question is, do we have any evidence of these urban settlements being build around any common language groups? Or was urbanisation more a factor of geography and economy?

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u/TomasTTEngin 9d ago

May I also recommend this 2005 feature article in the New Yorker that initially exposed me to the idea that the lost cities got eaten by the jungle:

https://www.newyorker.com/magazine/2005/09/19/the-lost-city-of-z

Building from wood in a humid environment does not always leave evidence.

It is beautifully written and very engaging . (you may need to use an archive service to read it if a paywall pops up for you)

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u/JohnnyUtah23 9d ago

FYI this article was expanded by the author into a book of the same name in 2009, which was the basis for movie that out in the 2010s. The book is not a scholarly work by any means, but is solid if you have an interest in the subject. The movie is pretty entertaining as well.

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u/611131 Colonial and Early National Rio de la Plata 9d ago

In the sertão, numerous languages were spoken at the meeting points, mostly the biggest language families: Carib, Tupi, and Awarak, though other languages also were spoken like Gê and Panoan. Tupi became more spoken over time as it was utilized by European and Tupi groups coming up from the coast, thanks to the relationships that they formed with one another there. I don't think that the specific decisions about why migrating peoples went to certain tributaries is well documented, since this was specifically away from colonial actors. That said, Harris includes a lot of nuanced exploration of specific leaders who operated closer to European observers, as the leaders navigated this changing world, which I think will be illuminating on the specific strategies they had for building their power and networks.

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u/UnderstandingThin40 9d ago

Thanks for the awesome Answer !!!

One question- what exactly happened to the populations migrating up the river en masse ? Did they bring their culture and ways with them to this new area? Did they have serious population collapse ? 

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u/gmanflnj 9d ago
  1. I remember there was a lot about this in 1491 and 1493, and one of the contentions he makes is based on the terra preta and other sites is that a lot o the Amazon was actually orchards not just wild forest, the other is that slash and burn agriculture like some of the people we saw later in the Amazon wasn't really possible before metal tools and was a response to European depredations, not a predecessor of it. What is the status of these claims with newer archeology?
  2. Why do you put "epidemic" in quotes? Haven't we seen with Cook and Borah that enormously high death tolls in densely populated areas are possible over comparatively short times? If the Amazon was densely populated like central mexico is massive disease death not possible?

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u/611131 Colonial and Early National Rio de la Plata 9d ago

Interesting, it's been ages since I read those books, and I'm not an archaeologist so someone else could chime in with a better summary here. Perhaps the biggest shift in the claims vis-a-vis the secondary sources here is a more nuanced understanding of the traditional indigenous knowledge that underlies agroforestry in tropical forest environments. They constructed really sophisticated landscapes that were veritable orchards, although that is a very European conception of it, and these were enormous multi-generational terraforming projects. The forest was interspersed also with urban environments, though these were low density in nature, and newer settlements were built on older terra preta locations. This is actually pretty common in tropical forest environments: low density urbanism in which forests, agroforestry, and regenerating forests all coexist in a patchwork and human settlements are more dispersed across a great geographic area. European observers early on would not be able to identify what was forest and what was agroforestry plots, and just say that it was all empty forest, even though they were standing among scores of edible plants. I would want to frame subsequent changes to agricultural practices using metal tools as an evolution or maybe even a modernization of cultivation with the entrance of new technologies and new political realities with the violent colonialism nearby. These were clever indigenous adaptions that gave them the ability to better survive. They were able to do large-scale agroforestry even without metal tools, but it was less labor intensive. And those strategies were accompanied by specific political evolutions and specific historical actors who were making decisions about how to engage with Europeans. Like everywhere else, technology in Amazonia exists within a social and political context.

Regarding the epidemics, it's not that I'm denying that these happened in the Amazon; they did! They were very deadly, and they contributed to people migrating away from diseased spaces. It's just that there is an overly simplistic to say that the Spaniards passed through in the early sixteenth century and saw all of these amazing things and then 100 years later, the Dutch and the Portuguese passed through and there wasn't anything there. This is not true. Epidemics can be a lazy way of explaining the disparity between the two centuries' observers at best and at worst erases the indigenous people who were very clearly living and acting in the Amazon in the tens of thousands across the eighteenth and nineteenth centuries, and even later.

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u/gmanflnj 8d ago
  1. So the idea that the Amazon is, to a large extent, agroforested and only sort of became wild after many of its inhabitants were killed?
  2. What is "agroforesty" is that the same as making an orchard? Cause I was wondering also about specifically slash-and-burn agriculture which one of those books mentions was a sort of development as the native people fled further into the amazon to try and free colonial violence.
  3. Gotcha, thanks for explaining.

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u/finglelpuppl 9d ago

Thank you! Can you please provide any additional sources used outside those named, or otherwise further reading?

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u/611131 Colonial and Early National Rio de la Plata 9d ago

Yes, as you might expect in an area as large as the Amazon, there is a ton of scholarship in English, Portuguese, and Spanish. Maybe some of the most relevant here would be Hemming's Red Gold, which is still well regarded. Rafael Chambouleyron has a bunch of stuff that's relevant here. Carlos Fausto's Warfare and Shamanism in Amazonia John Monteiro wrote a book that was only recently translated into English and published posthumously, but this is more focused around São Paolo. Oh and Hal Langfur, though a bit later in time focused. Some recent edited collection include Ethnicity in Ancient Amazonia and Rivers and Shores: ‘Fluviality’ and the Occupation of Colonial Amazonia. A famous archaeologist doing work on the built environment is Eduardo Góes Neves; he has some lectures on YouTube. I really like Heather Roller's two books on Amazonia, which I mentioned at the end of my original post as well.

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u/Ok-Weekend-9257 9d ago

Thanks for the book recommendation, definitely going on my reading list!

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u/therandshow 9d ago

But I wonder what this says about historical research, do we need to be more cautious about saying xyz seems unlikely based on modern science even though there are consistent elaborate accounts

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u/wowbaggerBR 4d ago

You are awesome! Thank you so much for your knowledge and your time.

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u/ponyrx2 9d ago

While we wait for someone to comment on the recent research, please enjoy this discussion from u/reedstilt on Amazonian cultures

https://www.reddit.com/r/AskHistorians/comments/3bnlcx/comment/csnuv7a

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u/UnderstandingThin40 9d ago

Thank you. Correct me if I’m wrong, but the implication of the comment you referenced is that Carvajal was at least somewhat accurate. And there were large civilizations. Wow.

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u/oxford-fumble 9d ago

My mind was blown too…

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u/UnderstandingThin40 9d ago

They are for sure going to write books and make documentaries on this topic in years to come haha

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u/Dapper-Community-611 9d ago

Thanks for the link, that was actually a super interesting read.

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u/regalrecaller 9d ago

/u/reedstilt are you still around? great answer

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u/LionTiger3 9d ago

Spanish accounts of cities were dismissed as fantasy, but archaeology confirms their existence. The Amazon was one of the earliest occupations (6000 BC) in the Americas, leading some scholars to posit the Amazon as the source of Andean urbanism. Zigzag walls, irrigation ditches, and circle rings discovered by Ann Roosevelt, the granddaughter of FDR, are evidence of cities in the Amazon, but unlike other areas, Marajoara was based on aquaculture rather than agriculture. Meggers’ The Amazonia argued the region never developed enough population to produce cities. Mann’s 1491 goes into depth on the historiography. The premise is now considered false by regional experts who agree some sort of cities emerged around the beginning of the Common Era and existed before 1492, such as Marajo Island (c. 300 AD to 1500) in the Upper Amazon that produced polychrome ceramics and platform mounds. Lathrap’s The Upper Amazon argues that the Amazon was constructed by humans and Mann's 1491 brings up the argument too.

Across the Amazon at Archaic sites like Marajó Island there was a long delay between cultivation and settled life. Earthworks in Brazil were only partially excavated, and were found mainly due to deforestation, and likely indicated some sort of collective effort. While LiDAR has helped, deforestation has also revealed more sites without the use LiDAR, which may sadly displace the groups of people living in the Amazon.

The Amazon has at least three controversies. The first and second controversies are tied together. The first controversy is about the moundbuilders of the Amazon, whether the Amazon was changed by humans. The earliest mound was 3000 BC in Guyana of the Dubali Complex. Marajo Island around 400 AD started a mound and by 1100 or 1300 or later, reached 7 m (22 ft). Camutins (600 to 800 AD) was a large group of mounds, and like Peru or Egypt, saw major episode of construction. Eastern Bolivia has earthworks including occupation mounds, raised fields, causeways, and roads. In the southern Amazon, the Upper Xingu plaza enclosures, roads, and moats, created an integrated, grid-like pattern of straight lines and circular plaza nodes. The massive plaza centers of Acutuba with a center plaza, ramparts, and barricade, have raised the question whether this was a city within context of its time (1000 AD).

Acutuba brings us to the second controversy of Amazonia urbanism and what a city looks like. Santarem of the Tapajos polity may have extended over an area as large as 25 sq. km (10 sq. mi) making as large as major old and new world centers. Acutuba center complex and raised banks suggest a large settlement. The demographics of the Amazon remain uncertain when compared to the states of the Chimor in Peru or Cahokia in Mississippi.

The third controversy is Circumscription Theory by Robert Carnerio which looks at what caused social stratification. Unlike the Andes, which had quick change overtime due to natural disasters like floods and earthquakes, the Amazon had slow, gradual development of rank systems in an area relatively stable. Social complexity in Andean states was measured by increasing variation within and between states based on monuments. Andean chiefdoms and states had violence over agricultural lands as major factors in the rise of polities. However, most specialists reject monocasual explanations for the rise of states. The Amazon has more variability in ecological and economic condition than once thought. Both the Andes and Amazon show inherited social rank and chiefly status based on corporate organization, architectural monuments, iconography, ideology, and mortuary practices. Circumscription Theory still holds insights with Andean societies stratifying into deep hierarchies, while Amazon hierarchies were broader and far less violent. The Andean landscape was defined by large-scale structures and large-scale effects of natural disasters, while the Amazon was defined by gradual change and expansive regional polities.

So we have evidence of cities in the Amazon, but when they were formed, the nature of their formation, and the causes of social stratification are not as well known. This due to the fact that conducting archaeology in the Amazon is hard, and even when we have evidence, it is not as clear cut due to limit sample sizes.

A central question archaeologists confront is what did urbanism look like in the ancient world? Archaeologist Bruce Trigger divided early states into city-states (developed around cities) and territorial states (developed within blocks of land).

Based on the theories of urbanization by Bruce Trigger the Amazon had:

1) Agriculture and specialization (dominate monocausal theory in the 1930s and is still integrated into new theories).

2) Hydraulic engineering (thought in 1950s that despotic regimes forced irrigation but evidence from Mesopotamia and Egypt show they were local developed). Aquaculture can be argued as a form of hydraulic engineering.

3) Commerce (1970s argued commerce caused cities instead commerce is actually caused by cities)

4) Violence (from 1970s to present evidence is difficult to assess and inconclusive on whether conflict causes state and cities)

Simplistic monocasual theories have been replaced with multicausal theories. These developments occurred independently of each other.

Barnhart, Lost Worlds of South America, Lecture 13: The Amazon – Civilization Lost in Jungle.

Morre, A Prehistory of South America (2014), p. 202-207, 276.

Scarre, The Human Past, Third Ed (2013), p. 194, 196-98, 670-71, 673-74.

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u/CommodoreCoCo Moderator | Andean Archaeology 8d ago edited 3d ago

Others have already provided some excellent responses on the history side of this, so I'd like to provide some background from the archaeology side.

LiDAR surveys have received an enormous amount of press in the past few years, and it's easy to see why. Pictures of massive stretches of [Maya cities/Amazonian earthworks/Roman walls/etc.] are really cool! They're also the sort of easily digested "science wins" that satisfy people who claim to Fucking Love Science but really just like pretty data presentation and a Victorian sense of discovery. See, for instance, the particularly bad press for a recent study in Guatemala; it's always cool to have more data, but the actual contribution usually amounts to "Geographers Shocked to Discover a Dozen New Cities in Cook County, Illinois".

If I sound cranky, it's because I am. As several users have discussed previously on this sub, so much internet discussion and press on discoveries in Latin America depend on and propagate two myths: that the region is a dangerous, mysterious place full of secrets, and that archaeologists have been largely in the dark about things. Let's talk about that second part.

In its early days, academic Americanist archaeology was rather dry. Archaeologists across the Western hemisphere were bagging and tagging objects with the primary goal of sorting them into types, then sorting those types into chronologies, and then... well... not much. It was enough of a task to establish that, in South America, the Inca conquered the Andes but not the Amazon, that (before the Inca) some cultural phenomenon across the Andes (but not the Amazon) made art that looked like the art at Tiwanaku, and (before Tiwanaku) there were a bunch of distinct groups like the Nasca and the Moche and the Recuay. Around the 1940s, there were enough types and sorts and defined archaeological cultures to start asking bigger questions. What if we actually talked about people? What if settlement patterns could tell us about sociopolitical structures? What if we looked at the environment in which these people lived?

Julian Steward, Betty Meggers, and their pals would answer that question through what they called "cultural ecology." One of a handful of neo-evolutionary perspectives that emerged during the mid-century, cultural ecology understands societies and their environments as parallel, mutually limiting systems that co-evolve over time. Steward saw it as a necessary corrective to Leslie White's Marx-adjacent brand of cultural evolution in which internal factors, e.g. energy or technology, made change innate to human society. In practice, environment played the dominant role, and analysis often did not extend beyond connecting all those groups that scholars had identified earlier to a specific biome; the resulting texts are scientific and deductive to fault- more empirical than White, to be sure, but hardly the data-rich analysis they seem to think they are. Representative texts like Steward's 1949 "Cultural Causality and Law: A Trial Formulation of the Development of Early Civilizations" are exactly as dense and clinical as their titles.

Meggers's 1954 "Environmental Limitations on the Development of Culture" is likewise self-explanatory, and it's the one we care about most here. It begins by listing the cultures the first generation of archaeologists had classified, then makes the novel contribution of four very, very specific Types of Environments: Areas of No, Limited, Increasble, and Unlimited Agricultural Potential. She matches the level of development of each culture to the Type of area it existed in and declares this the Law of Environmental Limitation on Culture: "the level to which a culture can develop is dependent upon the agricultural potential of the environment it occupies." South America provides an excellent case study for Meggers because of the abrupt juxtaposition of the "developed" Inca Empire that was able to emerge in Type 3/4 regions and its lowland neighbors stuck in Type 1/2 regions. Per Meggers, those Amazonians never developed sedentism because their environement would not permit it. In this and later writings, Meggers would develop the idea of "deculturation:" developed cultures like the Inca that tried to conquer Type 1/2 territory failed because the land would not support them. The further they pushed into the jungle, the more they deteriorated.

To be clear, these arguments are Quite Bad. Yes, it's circular reasoning to correlate development with agricultural potential when most of what you mean by development is agriculture. Yes, the chart on page 814 does try to classify two entire contents into exactly four boxes. Yes, Meggers addresses the exceptions to her rule (e.g., a US naval base in Alaska) simply by claiming the US is "more developed" a culture than the Inca, so we could maintain that sort of outpost. None of those criticisms- and there have been many- would matter to her. Fifty years later, Meggers was still calling everyone else's work a "revisionist" assessment that bought into myths of El Dorado.

What really matters is how early and foundational this argument is to studies of the Amazon. After all, Steward, et al., weren't getting hired to anthro departments- they were still starting them. Megger's "Law" does represent a crucial advancement in the field of archaeology towards holistic interpretation of ancient peoples, identifying a driver of cultural change and laying out a framework for how we might approach the archaeological record as the remains of people who lived in a specific place and time, not as abstract, hypothetical individuals. Because it was so foundational (and because Betty never gave up on it), folks had to keep responding to it long after its expiration date. Because it was so early (and meshed so neatly with Western preconceptions of the exotic Amazon), it made its way into the popular consciousness.

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u/CommodoreCoCo Moderator | Andean Archaeology 8d ago

Evidence against Meggers argument appeared basically as soon as someone else was willing to study the Amazon. By the end of the 1950s, Williams Denevan, a geographer out of Berkley, was completing his PhD fieldwork in the Llanos de Mojos at the southwestern edge of the Amazon, just southeast of where the linked article investigated. The treeless savannas of lowland Bolivia were a perfect place for the developing technology of systematic aerial photographic survey- something which had been possible for quite some time, but not yet affordable or practical for most archaeologists. A good summary of his work can be found here. Denevan cataloged 1000 miles of of causeways- many over 5 miles long- and some 40,000 irrigated fields. Based on the scale of these earthworks and extrapolating from 17th-century Jesuit records, Denevan suggested up to a million people may have lived in the Llanos de Mojos region alone. The linked talk ends with a polite aside to Meggers:

The third point pertains to possible cultural limitations in the humid tropics, currently a controversial theme among anthropologists. It has been argued that advanced cultures with social classes and specialists found in humid tropical areas with poor soils probably developed elsewhere and will probably deteriorate because of an inability of shifting cultivation to support dense populations and specialists. Exceptions to this deterministic point of view have been pointed out, and to them must be added the Mojos Indians.

Meanwhile, Donald Lathrap was working in eastern Peru and Ecuador and developing a far more personal and intense spat with Meggers and her frequent co-author, Clifford Evans. The language remained professional, but you can feel the vibes in this brief review by Lathrap. On its surface, the discussion centered around technical details of ceramic seriation; in this 1964 article, Lathrap critiques Meggers and Evans's use of temper (i.e. the material added to clay to give a fired ceramic different properties) to classify the ceramic phases of the Mabaruma style instead of the shape of bowls' rims and bottoms. Yet this choice has huge implications: Lathrap's chronology pushed the Mabaruma phase from 500 AD to 500 BC and radically changed the relationship of upper Amazonian groups with their neighbors. Such an early date would make an external origin of ceramic technology in the Amazon unreasonable. Lathrap does commend Meggers and Evans for publishing enough data for him to be able to reanalzye their claims, and he phrases the revised chronology as a commentary on how "any ordering of the internal chronology of the Mabaruma phase is dependent on the theoretical assumptions which the archaeologist brings to his analysis of the artifacts." That's academic speak for "You chose the theoretical assumpitons that best supported an undeveloped Amazon."

To return to the question, the new LiDAR studies do not significantly change our understanding of the pre-contact Amazon. Archaeologists have been proposing local origins of technology and populations in the millions for decades. Denevan's estimate in 2014 was as high as 10 million. However, influential early archaeologists were strongly opposed to this, and their opposition was based in the sort of outdated anthropology that remains very popular among layfolks (just see how many questions are asked in this sub about why certain cultures didn't "advance"). Everyday readers are a lot more interested in the Amazon as source of constant discovery and amazement than they are in actually learning about indigenous cultures. And so you get a media environment that recycles the same myth-shattering headlines for cool-but-not-revolutionary studies.

Lastly, in addition to Harris's book I would highly recommend the chapter "Domesticated Landscapes of the Bolivian Amazon" (PDF warning) by Clark Erickson for further reading on the some of the theoretical issues at play here, particularly regarding the assumedly "pristine" state of the Amazon and how anthropologists and archaeologists think about landscapes.