A rack of human skulls underneath Mexico City's cathedral affirms the truth of an ancient rumor: the Aztecs had a large-scale industry of human sacrifice.

Discovery Of A Tzompantli

Archaeologists first uncovered the remains of a tzompantli, a rack of human skulls flanked by two towers of even more skulls in 2015. A construction project at the heart of modern-day Mexico City called for archaeologists to do an excavation at the site of the Templo Mayor, an Aztec pyramid that was the political and religious center of the empire based in the capital Tenochtitlan.  

Over the last three years of examining the site, a team of archaeologists at the National Institute of Anthropology and History have concluded that their discovery constitutes one of the most astounding proofs of the massive extent of human sacrifice done by the Mexica people, the rulers of the Aztec Empire, which lasted from the 14th to 16th centuries.

The rack itself is said to be 35 meters long and up to 14 meters wide, larger than a basketball court. It towered up to 5 meters high and had two side towers that were 1.7 meters tall and 5 meters in diameter. The structure is placed in front of the Templo Mayor and its two temples, one for the war god Huitzilopochtli and the other to the rain god Tlaloc.

Between the rack and the two towers, the archaeologists estimate thousands of humans were sacrificed to the Aztec gods to provide the skulls used to build the structure.

Who Were The Victims?

At least 180 almost intact skulls and thousands of skull fragments were recovered from the site, which is now being studied by a team led by archaeologist Jorge Gomez Valdes of INAH.

Scribes of the Spanish conquistadors who eventually destroyed Templo Mayor and the tzompantli in front of it said the victims were prisoners of war, likely those from rival state Tlaxcala. Others were slaves sold for the express purpose of being sacrificed. The empire's subjects were also made to send tributes for sacrifice, as a way to subdue the population.

Valdes's team says 75 percent of the victims were men, aged 20 to 35 years old, the prime warrior age. Another 20 percent were women, while 5 percent were children. An analysis of smaller offerings done inside the temple itself by Ximena Chavez Balderas, also of INAH, shows that although the victims were born in various parts of Mesoamerica, they lived in the capital for a while before their death.

"They aren't foreigners who were brought into the city and directly to the ritual," she says. "They were assimilated into the society of Tenochtitlan in some way."

The Human Sacrifice Ritual

Each of the skulls bear precisely drilled holes on the sides of its head, which was used for holding it in place on the tzompantli. By studying the size and shape of these holes, the archaeologists were able to piece together a gruesome picture of how the sacrifice ritual took place.

An Aztec priest, displaying an acute knowledge of the human anatomy, would use a razor-sharp obsidian blade to cut open the victim's torso and take his still beating heart. The body would then be carried to a ritual space and set face up so that the priest could make the precise slash between two bones in the neck to cut off the head.

"[Mexica priests] had extremely impressive anatomical knowledge, which was passed down from generation to generation," says Chavez Balderas.

The priest would then carve away the flesh of the head until only the skull remains. He would then cut a hole into the sides of the skull and insert the skull into a thick wooden post, where it would hang with other skulls. After months of exposure to sun and rain, some of the skulls would have broken down. These would then be used to make masks offered to gods or build the two towers on the sides of the rack.  

The Purpose Of Human Sacrifice

The Aztecs, like many ancient peoples in Asia and Europe, believed that sacrificing human lives was nourishment to their gods. For them, it was the ultimate ritual that ensured humanity's existence. They believed that sacrificial victims were given a special place in the afterlife. However, the Mexica people favored an excess of human sacrifice.

"The Mexica certainly brought this to an extreme," says bioarchaeologist Vera Tiesler of the Autonomous University of Yucatan. "Tenochtitlan was the maximum expression [of tzompantli tradition]."

Social scientists believe painful offerings, such as that of thousands of human lives, can build up a society's group identity, especially in larger, more complex groups. It is also a way for the society's rulers to reinforce hierarchy.