Archaeologists guided by laser images of a remote region of northern Guatemala have discovered 20-foot-high walls, watchtowers, and other evidence that ancient Maya societies waged large-scale warfare over many years. The finds have upended long-established impressions of a civilization that tamed the jungle and built thriving cities, then declined and disappeared beneath the dense tropical forest.

Among the most startling discoveries was a large fortress complex now called La Cuernavilla. Built on a steep ridge between the Maya cities of El Zotz and Tikal, the heavily fortified site included high walls, moats, watchtowers, and caches of round stones that likely served as ammunition for warriors’ slings. It is the largest defensive system ever discovered in the region, “and possibly in all