A Mayan city lost in the dense jungle of southern Mexico has been revealed. The discovery occurred in the southeastern state of Campeche, and archaeologists have named it Valeriana, after a nearby freshwater lagoon.

“The larger of Valeriana’s two monumental precincts has all the hallmarks of a classic Mayan political capital: enclosed plazas connected by a broad causeway; temple pyramids; a ball court; a reservoir formed by damming an arroyo (a seasonal watercourse); and a probable E-Group assemblage, an architectural arrangement that generally indicates a founding date prior to AD 150,” says the study, published in the journal Antiquity.

The city’s discovery didn’t require breaking through the jungle with machetes or patiently excavating with brushes and spatulas. Nor did researchers need tape measures, binoculars, or compasses to find their way through the thick foliage. Instead, they employed state-of-the-art technology: lasers, drones, and satellite maps. With these tools, they discovered a city hidden for centuries beneath the thick Mexican jungle, unearthing pyramids, enclosed plazas, and an ancient reservoir.

Luke Auld-Thomas, an anthropologist at Northern Arizona University, made the discovery. His analysis revealed a huge network of previously unexplored settlements.

Auld-Thomas and his fellow researchers have succeeded in mapping the city beneath the jungle thanks to airborne laser scanning, better known as lidar (light detection and ranging), a remote-sensing technique that uses pulsed lasers and other data collected through flyovers that can generate accurate three-dimensional models of surface features, revolutionizing the way archaeologists explore the hidden past.

Laser pulses generate a topographic map in a manner similar to how a bat uses echolocation: Laser light is fired from an aircraft, bounces off objects on the ground, and returns to the detector located on the underside of the aircraft. In Mexico, although only a small fraction of the pulses pass through the dense jungle, the large number of pulses emitted allows enough light to reach the ground, creating a map with a resolution of up to 1 meter. Based on the timing and intensity of the returning pulses, the detector can map the contours of the terrain, revealing hills, ditches, and ancient ruins covered in vegetation. The technology is also being integrated into autonomous cars to help them avoid crashes.

“For a long time, our understanding of the Mayan civilization was limited to an area of a few hundred square kilometers,” Auld-Thomas says. “This limited sample was obtained with great effort, with archaeologists painstakingly scouring every square meter, hacking away at vegetation with machetes, only to discover they were standing on a pile of rocks that might have been someone’s house 1,500 years ago.”

While Auld-Thomas knew that lidar could be a valuable tool, he was also aware of its high cost. Funders are often reluctant to invest in lidar surveys in areas where there is no visible evidence of Mayan settlement, despite the fact that this civilization reached its peak between 250 and 900 AD.

Campeche: A Center of Dense Urbanization Since the Mayan Era

In this case, the lidar data was originally collected over a decade ago, for completely unrelated purposes. The scans were completely in 2013 by the Mexican firm CartoData, using a Riegl LMS-Q780 sensor. Processing was carried out by the Woods Hole Research Center (WHRC), and the data was made publicly available a few years later by the M-REDD+ Alliance.

The dataset includes three transects and three study blocks. The transects have an approximate width of 275 meters and a total length of 213 kilometers, covering an area of 58.3 square kilometers. The survey blocks cover a total area of 64.1 square kilometers, distributed in three locations: south of the town of Xpuhil, near the archaeological site of Río Bec; near the villages of Dos Lagunas and Bel Ha; and near the town of Ucum, in northern Campeche.

The study mentions that the analysis of 6,764 structures in the lidar data blocks reveals a settlement density of 55.3 structures per square kilometer, comparable to other research in the region. These data are useful for assessing settlement density on a regional scale and exceed values recorded in Belize and Guatemala. However, they do not provide a complete picture of the level of urbanization, which requires analysis of local variability and density gradients. For this purpose, a kernel density estimation was applied to the study blocks, the results of which are consistent with the densities recorded in other Mayan archeological sites such as Oxpemul and Becan.

Archeologists in the 20th century were correct in stating that the interior of Campeche is a substantially anthropogenic landscape, i.e., human-modified, with urbanized areas where rural populations interacted with dense cities. Settlement density data, ranging from 49 to 61 structures per square kilometer, indicate that cities and dense settlements are common in large parts of the central Maya lowlands. New discoveries, such as the city of Valeriana, reinforce this view, showing that urbanization was a widespread phenomenon in the region.

Archaeologists increasingly recognize that the world’s tropics and subtropics hosted a wide variety of urban forms in antiquity. Many of these settlements followed a pattern of spatial dispersion, commonly called “low-density urbanism.” However, it is now being recognized that these urban landscapes were not uniform, but exhibited significant variations in settlement density, both within and around cities and between subregions.

At the same time, the growing body of research has revealed a greater abundance of settlements and cities than had previously been contemplated. This has generated a tension between two developments: On the one hand, the recognition of high variability in settlement density and, on the other, evidence of a more densely urbanized past than previously thought.

Although lidar was developed in the 1960s to study clouds and atmospheric particles, its application in archaeology is relatively recent. It was not until the last decade that archaeologists began employing it to unearth hidden landscapes. In 2009, archaeologists Diane and Arlen Chase of the University of Nevada, Las Vegas, pioneered the use of lidar to map a Mayan city, revolutionizing the way ancient civilizations are detected and studied.

According to the study, some researchers argue that the discovered landscapes reflect a high population density, while others suggest that the surveys are biased and overrepresent the most densely populated areas. This leaves open the question of whether as yet unexplored areas could confirm the existence of a higher urban density or show less dense occupation.

This story originally appeared on WIRED en Español and has been translated from Spanish.