Skulls reveal massive scale of human sacrifice in Aztec city

The priest quickly sliced into the captive's torso and removed his still-beating heart. That sacrifice, one among thousands performed in the sacred city of Tenochtitlan, would feed the gods and ensure the continued existence of the world.

Death, however, was just the start of the victim's role in the sacrificial ritual, key to the spiritual world of the Mexica people in the 14th to the 16th centuries.

Priests carried the body to another ritual space, where they laid it face-up. Armed with years of practice, detailed anatomical knowledge, and obsidian blades sharper than today's surgical steel, they made an incision in the thin space between two vertebrae in the neck, expertly decapitating the body. Using their sharp blades, the priests deftly cut away the skin and muscles of the face, reducing it to a skull. Then, they carved large holes in both sides of the skull and slipped it onto a thick wooden post that held other skulls prepared in precisely the same way. The skulls were bound for Tenochtitlan's tzompantli, an enormous rack of skulls built in front of the Templo Mayor—a pyramid with two temples on top. One was dedicated to the war god, Huitzilopochtli, and the other to the rain god, Tlaloc.

Eventually, after months or years in the sun and rain, a skull would begin to fall to pieces, losing teeth and perhaps even its jaw. The priests would remove it to be fashioned into a mask and placed in an offering, or use mortar to add it to two towers of skulls that flanked the tzompantli. For the Aztecs—the larger cultural group to which the Mexica belonged—those skulls were the seeds that would ensure the continued existence of humanity. They were a sign of life and regeneration, like the first flowers of spring.

But the Spanish conquistadors who marched into Tenochtitlan in 1519 saw them differently. For them, the skulls—and the entire practice of human sacrifice—evinced the Mexica's barbarism and justified laying waste to the city in 1521. The Spanish tore down the Templo Mayor and the tzompantli in front of it, paved over the ruins, and built what would become Mexico City. And the great rack and towers of skulls passed into the realm of historical mystery.


"This is a world of information," says archaeologist Raùl Barrera Rodríguez, director of INAH's Urban Archaeology Program and leader of the team that found the tzompantli. "It's an amazing thing, and just the kind of discovery many of us had hoped for," agrees John Verano, a bioarchaeologist at Tulane University in New Orleans, Louisiana, who studies human sacrifice. He and other researchers hope the skulls will clarify the role of large-scale human sacrifice in Mexica religion and culture—and whether, as scholars suspect, it played a key part in building their empire.


Much of the temple had survived to be discovered. The Mexica built it in seven phases between 1325 and 1521, each corresponding to the reign of a king. Each phase was built over and around the earlier ones, embedding the Templo Mayor's history within it like a set of Russian nesting dolls. Although the Spanish destroyed the temple's final phase, the smaller temples from earlier reigns were paved over but left relatively unscathed. Those ruins are now part of the Templo Mayor Museum. But many structures that surrounded the ruins remained hidden beneath the dense colonial city—and now, the modern megalopolis.

So when Barrera Rodríguez got the call to excavate a site just a few buildings down from where Guatemala Street dead-ends into the Templo Mayor complex, he knew the dig could lead to a major discovery. Starting in February 2015, his team dug about 20 test pits, unearthing modern debris, colonial porcelain, and, finally, the basalt slabs of a Mexica period floor. Then, he remembers, "Hundreds of skull fragments began to appear." In more than 2 decades of excavating in downtown Mexico City, he had never seen anything like it.

Barrera Rodríguez and INAH archaeologist and field supervisor Lorena Vázquez Vallín knew from colonial maps of Tenochtitlan that the tzompantli, if it existed, could be somewhere near their dig. But they weren't sure that's what they were seeing until they found the postholes for the skull rack. The wooden posts themselves had long since decayed, and the skulls once displayed on them had shattered—or been purposely crushed by the conquistadors. Still, the size and spacing of the holes allowed them to estimate the tzompantli's size: an imposing rectangular structure, 35 meters long and 12 to 14 meters wide, slightly larger than a basketball court, and likely 4 to 5 meters high. From their knowledge of the eras of the Templo Mayor, archaeologists estimate that the particular phases of the tzompantli they found were likely built between 1486 and 1502, although human sacrifice had been practiced in Tenochtitlan since its founding in 1325.
Sacrifice city

Nearby, the researchers also found skulls apparently stuck together with mortar—remnants of one of the towers flanking the tzompantli, where most skulls once exhibited on its posts ended their postmortem journey. The team spent a second season, from October 2016 to June 2017, excavating the tzompantli and the tower. At its largest, the tower was nearly 5 meters in diameter and at least 1.7 meters tall. Combining the two historically documented towers and the rack, INAH archaeologists now estimate that several thousand skulls must have been displayed at a time.

Other Mesoamerican cultures also engaged in human sacrifice and built tzompantlis. But, "The Mexica certainly brought this to an extreme," says Vera Tiesler, a bioarchaeologist at the Autonomous University of Yucatán in Mérida, Mexico. In her work at the Mayan city of Chichen Itza, founded some 700 years before Tenochtitlan and more than 1000 kilometers away, she found six skulls with holes in their sides that she suspects were once displayed on the posts of a tzompantli. However, the holes in each skull were less regular and uniform than those in the Tenochtitlan skulls. "That makes me think it was not a standardized practice yet," she says. "Tenochtitlan was the maximum expression [of the tzompantli tradition]."

Human sacrifice occupied a particularly important place in Mesoamerica. Many of the region's cultures, including the Maya and the Mexica, believed that human sacrifice nourished the gods. Without it, the sun would cease to rise and the world would end. And sacrificial victims earned a special, honored place in the afterlife.

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Many researchers say that, for the Mexica, political power as well as religious belief is likely key to understanding the scale of the practice. Theirs was a relatively young empire; during their 200-year reign, they conquered territory all over central and southern Mexico, sometimes facing tremendous resistance from local communities (some of which would later ally with the Spanish against the empire). Spanish chronicles describe Tenochtitlan's sacrificial victims as captives brought back from wars, such as those fought with their archenemy, the nearby republic of Tlaxcala. Subject peoples in the Mexica Empire were also sometimes required to send individuals as tribute. "The killing of captives, even in a ritual context, is a strong political statement," Verano says. "It's a way to demonstrate power and political influence—and, some people have said, it's a way to control your own population."

"The more powerful a state was, the more victims it could dedicate," says Ximena Chávez Balderas, an INAH bioarchaeologist who spent years studying the remains of sacrificial victims in offerings in the Templo Mayor; she is now Verano's doctoral student at Tulane. The religious significance and political messaging of human sacrifice "go hand in hand," she says.

Over two seasons of excavations, INAH archaeologists collected 180 mostly complete skulls from the tower as well as thousands of skull fragments. Now, those finds sit in a lab next to the Templo Mayor ruins, being painstakingly examined by a team led by INAH anthropologist Jorge Gómez Valdés. Cut marks on the skulls leave no doubt they were defleshed after death, and the decapitation technique appears clean and uniform. "[Mexica priests] had extremely impressive anatomical knowledge, which was passed down from generation to generation," Chávez Balderas says.

Gomóz Valdás found that about 75% of the skulls examined so far belonged to men, most between the ages of 20 and 35—prime warrior age. But 20% were women, and 5% belonged to children. Most victims seemed to be in relatively good health before they were sacrificed. "If they are war captives, they aren't randomly grabbing the stragglers," Gómez Valdés says. The mix of ages and sexes also supports another Spanish claim, that many victims were slaves sold in the city's markets expressly to be sacrificed.

Chávez Balderas identified a similar distribution of sex and age in her studies of victims in smaller offerings within the Templo Mayor itself, which often contained skulls from the tzompantli that had been decorated and turned into eerie masks. Her colleagues also analyzed isotopes of strontium and oxygen that the teeth and bones had absorbed. The isotopes in teeth reflect the geology of a person's surroundings during childhood, whereas isotopes in bones show where a person lived before death. The results confirmed that the victims were born in various parts of Mesoamerica but had often spent significant time in Tenochtitlan before they were sacrificed. "They aren't foreigners who were brought into the city and directly to the ritual," Chávez Balderas says. "They were assimilated into the society of Tenochtitlan in some way." Barrera Rodríguez says some historical accounts record cases of captive warriors living with the families of their captors for months or years before being sacrificed.

Samples for isotopic analysis as well as ancient DNA studies have already been taken from many of the tzompantli skulls, Gómez Valdés says. He, too, expects to find a diversity of origins, especially because the tzompantli skulls display a variety of intentional dental and cranial modifications, which were practiced by different cultural groups at different times. If so, the skulls could yield information that extends far beyond how the victims died. "Hypothetically, in this tzompantli, you have a sample of the population from all over Mesoamerica," Vázquez Vallín says. "It's unparalleled."