In 2007, archaeologist Christopher Morehart was using satellite imagery to map the irrigation canals and waterways surrounding the ancient city of Teotihuacan, in Mexico.
The researchers began investigating a region about 15 miles from the ancient city that had once housed a vast lake called Lake Xaltocan.
The team noticed evidence of looting and began excavating. When they dug further, they found a shocking discovery.
The site contained dozens of skulls lined up, all severed at the first or second vertebrae.
The site also contained a shrine with several artifacts associated with agricultural culture.
The combination of artifacts and human remains led the researchers to conclude that a mass human sacrifice occurred at the site.
Carbon dating of the skulls and a nearby incense burner led the team to conclude the skulls date to between 600 to 850 A.D., around the time of Teotihuacan's fall.
So far, the team has excavated over 150 skulls. (The researchers chose not display the skulls because the sacrificed people may have historic ties to people of today's indigenous cultures.)
An artifact depicting Tlaloc, an ancient water god from the Pre-Columbian period in Mexico, was found at the human sacrifice site at Lake Xaltocan.
Because of its rural locale, the sacrifice event is markedly different from others in the region, which typically took place in the great pyramids of large cities
The sacrifice likely occurred during a time of great upheaval, when the Teotihuacan culture was declining