The Maya population during the civilization’s peak 1,400 years ago may have been far larger than previously thought, new research reveals. The study also hints that Maya settlements at that time were far more complex and interconnected than prior studies had suggested.

A 2018 study estimated there were 11 million Maya between A.D. 600 and 900, known as the Late Classic Period. But in new research published online in the Journal of Archaeological Science: Reports, some of the 2018 study’s authors have revised the estimate to 16 million.

Both studies estimated the Maya population size using lidar (light detection and ranging) data, which is obtained with an aircraft carrying a machine that shoots laser pulses at the ground to create 3D maps of an area. The ruins of buildings on these maps can provide clues about population density, which researchers can extrapolate to come up with a total population count. “We expected a modest increase in population estimates from our 2018 lidar analysis, but seeing a 45% jump was truly surprising,” Francisco Estrada-Belli, a research professor in the Middle American Research Institute at Tulane University in Louisiana and the new study’s lead author, said in a statement. “This new data confirms just how densely populated and socially organized the Maya Lowlands were at their peak.”

The Maya Lowlands are swathes of forested land that include parts of modern-day Guatemala, Belize and Mexico. Specifically, the researchers created lidar maps for 36,700 square miles (95,000 square kilometers) of land in Guatemala’s Petén department, western Belize, and the Mexican states of Campeche and Quintana Roo.

The Maya civilization peaked between A.D. 250 and 900, with numerous cities thriving in Mesoamerica during that time. Researchers have long thought that, aside from these cities, the civilization was limited to scattered settlements interspersed with farmland in the region’s sprawling tropical rainforests.

However, the new research shows that Maya settlements were far more complex and interconnected than previously thought. “We’re confident these lidar-based findings give us the clearest picture yet of ancient Maya settlement patterns,” Estrada-Belli said. “We now have hard evidence that Maya society was highly structured across both cities and rural areas and far more advanced in resource and social organization than previously understood.”