An ongoing excavation in the heart of Mexico City, once the great Aztec capital Tenochtitlan, has revealed a legendary tower inlaid with hundreds of skulls. This tower was first described by Europeans in the early 16th century, when a Spanish soldier named Andres de Tapia came to the city with Hernan Cortez' invading force. In his memoirs, de Tapia described an "edifice" covered in tens of thousands of skulls. Now his account is corroborated by this historic find.

According to a report from Reuters, the tower is 6 meters in diameter, and once stood at the corner of a massive temple to Huitzilopochtli, an Aztec god associated with human sacrifice, war, and the sun. It's likely the tower was part of a structure known as the Huey Tzompantli, which many of de Tapia's contemporaries also described.

Tzompantli were ceremonial wooden scaffolds used in many ancient cultures of the Americas to display the skulls of human sacrifices. Priests would prepare each skull by drilling two holes in it, then stringing it like a bead on a long cord. Once a set of skulls had been strung together, the cord would be stretched between two wooden posts, to form one row of skulls among many. The sight was designed to terrify the Aztec's enemies, and it certainly worked in the case of Spanish soldiers. Many recorded their terror upon seeing tzompantli in Tenochtitlan.

National Institute of Anthropology and History (INAH) archaeologist Raul Barrera told Reuters that "the skulls would have been set in the tower after they had stood on public display on the tzompantli." It appears that the skulls were coated in lime and sunk into the wall of the tower in tidy rows.

Archaeologist Lorena Vazquez, also from INAH, told the BBC what the tower might have looked like 500 years ago: "In this context where there are many semi-detached skulls, and where you are also seeing a tower on each side made up of skulls, it must have been shocking for the people who saw it."

The recent excavation has also revealed that the skulls came from men, women, and children. This suggests that the people sacrificed here were not just soldiers, who would have primarily been men. Instead, human sacrifices for the tower came from a cross-section of the population.

Archaeologists have not yet reached the base of the tower in their dig. You can expect more discoveries as excavations continue at this site near the Aztecs' grand Templo Mayor.

Listing image by Henry Romero/Reuters