A chilling find deep under old Mexico City has experts rethinking the Aztec practice of human sacrifice, Reuters reports. Archaeologists who discovered a tower of more than 650 skulls and fragments were stunned to see the crania of women and children. The new find is believed to be part of the Huey Tzompantli, a fabled tower of skulls that terrified the conquistadores, the BBC notes. A soldier who was part of Cortes' conquest of Mexico in 1521 noted tens of thousands of skulls, thought to be the severed heads of captured warriors. The team of diggers who began their work below the Metropolitan Cathedral in 2015—once the site of the Aztec Templo Mayor—expected to find the skulls of "just men, obviously young men, as warriors would be," says archaeologist Rodrigo Bolanos.
But finding the skulls of women and kids added a whole new twist to the Aztec practice of human sacrifice made as an offering to the sun. "Something is happening that we have no record of, and this is really new," Bolanos adds. The skulls would have been formed into the creepy tower, around 19.5 feet in diameter, after a period of public display. It was once part of the chapel of Huitzilopochtli, Aztec god of the sun, war, and human sacrifice. So far, the team has found 676 skulls and the excavation is continuing. (Digging for Rome's new subway was described as a "Pompeii-like scene.")