Classic Maya civilization in detail 
 
 Lidar (a type of airborne laser scanning) provides a powerful technique for three-dimensional mapping of topographic features. It is proving to be a valuable tool in archaeology, particularly where the remains of structures may be hidden beneath forest canopies. Canuto et al. present lidar data covering more than 2000 square kilometers of lowland Guatemala, which encompasses ancient settlements of the Classic Maya civilization (see the Perspective by Ford and Horn). The data yielded population estimates, measures of agricultural intensification, and evidence of investment in landscape-transforming infrastructure. The findings indicate that this Lowland Maya society was a regionally interconnected network of densely populated and defended cities, which were sustained by an array of agricultural practices that optimized land productivity and the interactions between rural and urban communities. 
 
 Science, this issue p. eaau0137; see also p. 1313 ||||| These crawls are part of an effort to archive pages as they are created and archive the pages that they refer to. That way, as the pages that are referenced are changed or taken from the web, a link to the version that was live when the page was written will be preserved.Then the Internet Archive hopes that references to these archived pages will be put in place of a link that would be otherwise be broken, or a companion link to allow people to see what was originally intended by a page's authors.The goal is to fix all broken links on the web . Crawls of supported "No More 404" sites. ||||| Earlier this year, a team of archaeologists announced the discovery of more than 61,000 long-lost Maya roads, fortresses, drainage canals, and buildings hidden beneath the dense green canopy of northern Guatemala’s tropical forest. The findings were the result of an airborne laser, or lidar, survey of 2,144 square kilometers of the Maya Biosphere Reserve. Now, archaeologists are starting to piece together what all the data actually says about Maya civilization. The picture emerging from beneath the jungle canopy is of a much more complex political and economic landscape than we previously realized. 
 
 “In February, you were really getting our first impressions as we began exploring the data, which was filmed by National Geographic. The Science article is about putting actual numbers behind those first impressions,” Ithaca College archaeologist Tom Garrison told Ars Technica. 
 
 A network of cities 
 
 Garrison, with archaeologists Marcello Canuto and Francisco Estrada-Belli of Tulane University and colleagues, used the lidar survey data to estimate that a Mayan population of between 7 million and 11 million people lived in the central Maya Lowlands (parts of the Yucatan, Guatemala, and Belize) in the bustling Late Classic Period between 650 and 800 CE. With 29 structures per square kilometer in the survey area, and evidence from earlier excavations to suggest how many of those structures might have been houses, the team calculated an average of 80 to 120 people per square kilometer. The overall number lines up well with estimates from previous studies, even though it was derived independently. 
 
 What archaeologists haven’t known for sure, because of the small-scale nature of most excavations so far, is how all those people clustered among the rolling karst and seasonal wetlands of northern Guatemala. With the large scale of the new survey, however, archaeologists can see a network of densely populated cities, connected by invisible bonds of trade and political affiliation that appear on the landscape as elevated roads between settlements. 
 
 That image supports the view that researchers have collectively leaned toward in recent years: the Maya were not a scattering of isolated, warring city-states living off slash-and-burn farms. They built urban centers supported by intensive farming of drained and irrigated lowland fields and carefully constructed upland terraces. The largest cities seem to be surrounded by smaller satellite cities and patches of rural territory, which Canuto and his colleagues say were probably connected politically and economically. 
 
 Maya breadbasket? 
 
 To support so many large cities, the Maya would have had to modify the landscape in more drastic ways than just clearing some trees; irrigating fields or draining wetlands would be essential. The fact that archaeologists have been estimating a population in that range for several years suggested that the Maya probably practiced more intensive farming, but archaeologists didn’t have enough data to say how widespread it was. 
 
 But in the lidar images, the ghostly outlines of channels reveal grids across the low seasonal wetlands, called bajos, where they would have served as a combination of irrigation channels and flood control. Most are one or two meters wide, between 20 and 50cm deep, and the longest stretch for a kilometer across the low-lying fields. In the uplands, lidar images revealed the long outlines of terraces and low field walls. 
 
 All told, about 17 percent of the survey area seems to have been farmland. But that varied from less than one percent in some blocks to as much as 70 percent around large cities like Tikal. Even with so much land under cultivation, and even with a lot of labor and infrastructure invested in getting the most out of the land, however, some of the larger Maya cities would have needed to rely on imported food to feed their people. 
 
 Canuto et al. 2018 
 
 Canuto et al. 2018 
 
 Canuto et al. 2018 
 
 Canuto et al. 2018 
 
 Trade and transport 
 
 “It is clear that some of the most densely settled cities, like Naachtun and Tikal, would not have been able to support their population with the land available to them,” Garrison told Ars Technica. “Other kingdoms, like Holmul, definitely had surplus. I suspect that yes, there was a certain degree of exchange of staple foods.” Further lidar surveys may help shed light on agricultural systems and which kingdoms controlled which chunks of farmland. 
 
 There's evidence of formal links between cities during earlier periods in Maya history in the form of elevated roads called causeways. These link many large cities with the smaller urban centers nearby; in a few cases, they link major cities to each other. These are broad roads, 10 or 20 meters wide, and the longest runs 22km through what was once farmland. 
 
 But most of the causeways that show up on the survey link cities that rose to prominence between 1000 BCE and 250 CE. Because archaeological evidence suggests that most Preclassic (1000 to 250 BCE) cities were abandoned by the Late Classic Period, Garrison says the causeways between them probably also fell into disuse. Sometimes that abandonment stood out in stark relief in the lidar images. 
 
 “In one interesting case from the lidar, agricultural terraces associated with the Classic-period kingdom of Xultun are constructed over a Preclassic causeway that had emanated out of the nearby site of San Bartolo,” he told Ars Technica. “In this case, the lidar is literally revealing the layering of settlement over time.” 
 
 Fortresses to withstand a siege 
 
 What the Maya were building during the Late Classic Period, however, were fortifications—and lots of them. Defensive systems of bridges, ditches, ramparts, and stone walls lie hidden beneath the foliage in greater numbers and at greater scale than Canuto and his colleagues expected, even though texts and archaeological evidence both portray the Maya as a militaristic, conflict-prone people. 
 
 “Their own writing gives sometimes vivid descriptions of war, in one case using hurricanes as a metaphor for the fury of battle, and in another describing its aftermath as the ‘piling of skulls and the pooling of blood,’” Garrison told Ars Technica. And archaeological work at Tikal and a few strategic points farther west has revealed some earthworks. 
 
 The defensive structures that showed up on the lidar survey, however, were much more common, and much more sophisticated, than most archaeologists had expected. And that suggests that Maya civilization must, at least at times, have engaged in warfare on an even larger scale than anyone thought. As evidence, Garrison points to a fortress revealed by the lidar survey, perched on the edge of an escarpment between Tikal and the nearby city kingdom of El Zotz. 
 
 “The citadel is protected by walls that are over 25 feet tall, and there is a large artificial reservoir that looks like an Olympic swimming pool. In other words, this place (named La Cuernavilla) was ready for a siege,” he told Ars Technica. “That is not really the type of conflict that we think about for the ancient Maya.” Garrison is about to begin a three-year excavation at La Cuernavilla. 
 
 Lasers in the air and boots on the ground 
 
 Many of the features that showed up in the lidar images are much harder to spot from the ground. Causeways, irrigation channels, and small defensive earthworks often leave a pretty subtle mark on the landscape after a few centuries, and their scale extends well beyond a person’s field of view in the dense jungle. “Even knowing a causeway is there and having lidar imagery loaded into my GPS, I still need to search carefully to be sure that I am in fact recognizing its edges,” Garrison told Ars Technica. 
 
 But there are still years’ worth of work to be done on the ground to confirm that what Canuto’s team saw in the digital images is actually there beneath the tropical forest canopy, a process archaeologists call ground-truthing. That process began before the survey even started; by choosing survey areas with known archaeological sites, the team could use those sites to help calibrate what they saw in the images. And more ground-truthing fieldwork started in 2017, shortly after the completion of the survey flights. 
 
 “In general, the lidar is extremely accurate, missing only the most subtle structures. There are occasional false identifications, but that seems to be restricted to certain types of terrain,” Garrison told Ars Technica. 
 
 Meanwhile, the survey has revealed some new sites for archaeology, such as Garrison’s upcoming work at La Cuernavilla, and provided a broader context for sites that have been excavated for years. And the broad view of the Maya landscape still leaves plenty of questions unanswered; there’s lots of detail to fill in on the big picture, and that detail may shape how archaeologists eventually interpret what they see in the lidar images. 
 
 And more large-scale views of the ancient landscape may be forthcoming, since the 2016 survey covered only portions of the Maya Biosphere Reserve. The Foundation for Maya Cultural and National Heritage, or Pacunam, has plans to cover most of the rest of the reserve in the coming years. 
 
 Science, 2018. DOI: 10.1126/science.aau0137 (About DOIs). ||||| More than 61,000 ancient Maya structures — from large pyramids to single houses — were lurking beneath the dense jungle canopy in Guatemala, revealing clues about the ancient culture's farming practices, infrastructure, politics and economy, a new aerial survey has revealed. 
 
 The Guatemalan jungle is thick and challenging to explore, so researchers mapped the terrain with the help of a technology known as light detection and ranging, or lidar. The lidar images were captured during aerial surveys of the Maya lowland, a region spanning more than 810 square miles (2,100 square kilometers). [See Photos from the Maya Lidar survey] 
 
 "Since lidar technology is able to pierce through thick forest canopy and map features on the Earth's surface, it can be used to produce ground maps that enable us to identify human-made features on the ground, such as walls, roads or buildings," Marcello Canuto, director of the Middle American Research Institute at Tulane University in New Orleans, said in a statement. 
 
 The aerial lidar survey covered 12 separate areas in Petén, Guatemala, and included both rural and urban Maya settlements. After analyzing the images — which included isolated houses, large palaces, ceremonial centers and pyramids — the researchers determined that up to 11 million people lived in the Maya lowlands during the late Classic period, from A.D. 650 to 800. This number is consistent with previous calculations, the researchers noted in the study, which was published online Friday (Sept. 28) in the journal Science. 
 
 It would have required a massive agricultural effort to sustain such a big population, the researchers said. So, it was no surprise when the lidar survey revealed that much of the wetlands in the area were heavily modified for farming, the researchers said. 
 
 A newly discovered site north of Tikal shows the range of features revealed by lidar. The long building (top right) is part of the so-called E Group complex, which largely dates to before 500 B.C. Across the valley from this building is an acropolis, which is likely 1,000 years younger. Credit: Luke Auld-Thomas/PACUNAM 
 
 In all, the surveys revealed about 140 square miles (362 square km) of terraces and other modified agricultural land, as well as another 368 square miles (952 square km) of farmland. 
 
 The lidar analysis (bottom) shows the hidden structures in the jungle of northern Guatemala (top). Credit: PACUNAM/Estrada-Belli 
 
 In addition, the lidar analysis uncovered 40 square miles (110 square km) of roadway networks within and between faraway cities and towns, some of which were heavily fortified. This finding highlighted the links between the Maya's hinterlands and urban centers, the researchers said. 
 
 "Seen as a whole, terraces and irrigation channels, reservoirs, fortifications, and causeways reveal an astonishing amount of land modification done by the Maya over their entire landscape on a scale previously unimaginable," Francisco Estrada-Belli, a research assistant professor of anthropology at Tulane University and director of the Holmul Archaeological Project, said in the statement. 
 
 Analyzing lidar terrain data can take months. Here, shaded relief terrain (left) can conceal important details, such as low mounds. More-complex visualizations, such as the red relief-image map (center) can make those details pop. But even more analysis is needed to identify and classify features (right). All three images show the site of Dos Torres, which is located between the cities of Tikal and Uaxactun. Credit: Luke Auld-Thomas and Marcello A. Canuto/PACUNAM 
 
 However, even though the lidar evaluation revealed so many previously unknown structures, researchers described it as a complement to, but not a replacement for, traditional archaeology. In a perspective article on the new research published in the same journal, Anabel Ford, an adjunct professor of archaeology at the University of California, Santa Barbara, and Sherman Horn, a visiting professor of archaeology at Grand Valley State University in Michigan, wrote that even with lidar, "boots on the ground" would always be needed. 
 
 Originally published on Live Science.
– Maya civilization was no mere collection of city states using slash-and-burn farming—that we learned earlier this year. Now archaeologists are looking deeper into an airborne survey that revealed a formidable civilization double the size of medieval England at its peak 1,200 years ago, Ars Technica reports. The survey, which used LIDAR (Light Detection And Ranging) to peek beneath the jungle foliage, revealed some 61,000 buildings, draining canals, fortresses, and roads across roughly 828 square miles. What archaeologists are saying about those details in Science: Population: About 7 million to 11 million people populated the central Maya Lowlands—an area including some of Belize, Guatemala, and Yucatan—between 650 and 800 CE, the Late Classic Period. How did researchers crunch that number? By counting the structures per square mile and estimating how many were houses. Big cities like Tikal likely had hundreds of people per square mile, per Discovery. Farming: A huge agricultural effort was needed to keep all those mouths fed, LiveScience notes. Imagine a complex grid of channels providing flood control and irrigation, with grids up to six feet wide and 20 inches deep, some stretching over half a mile. Still, densely populated cities like Naachtun and Tikal had to import food from other Maya kingdoms to survive. Causeways: In earlier Maya times, from 1000 to 250 BCE, cities were linked by elevated roads or causeways up to 65 feet wide and up to 13 miles in length—but they fell into disuse when so-called Preclassic cities were abandoned. Yet their faded ghost outlines are visible on the LIDAR. Fortresses: Mayans built more of them than expected in the Late Classic Period, and sophisticated ones, too. One has walls over 25 feet high and an Olympic-pool-size reservoir: "In other words, this place was ready for a siege," says Ithaca College archaeologist Tom Garrison. "That is not really the type of conflict that we think about for the ancient Maya." Overall: "Seen as a whole, terraces and irrigation channels, reservoirs, fortifications, and causeways reveal an astonishing amount of land modification done by the Maya over their entire landscape on a scale previously unimaginable," a Tulane researcher says in a statement.