Fifteen hundred years ago, Mexico’s Teotihuacan was a multicultural metropolis, enlivened by the diverse dress, foods, and dialects of its immigrant groups. Artifacts show the city of more than 100,000 depended on a steady stream of foreigners, who brought skilled labor and exotic goods from across Mesoamerica. But after Teotihuacan faded, during a period of upheaval and uncertainty, locals may have turned against outsiders—and archaeologists now think they’ve found the decapitated heads to prove it.
The study is “a major contribution” to our understanding of migration in ancient Mesoamerica and violence following Teotihuacan’s collapse, says Sarah Clayton, an archaeologist at the University of Wisconsin, Madison, who was not involved in the research.
Ritual killing was part of political and religious life in ancient Mesoamerica. Rulers held mass sacrifices atop imposing monuments at the heart of urban centers, such as Teotihuacan’s Pyramid of the Feathered Serpent or the later Aztec Empire’s Templo Mayor in Tenochtitlan. The victims generally included locals, immigrants, and captive warriors.
But in 2007, while searching for ancient farms about 40 kilometers northeast of Mexico City, Arizona State University (ASU), Tempe, archaeologist Christopher Morehart discovered a different kind of sacrificial site: a humble patch of ground littered with bits of bone and pottery. Excavations revealed a shoddy limestone platform, packed with incense burners, deity figurines, and severed skulls from at least 180 individuals. The rest of the skeletons were missing—except for the topmost vertebrae, as well as some finger and toe bones tucked into eye sockets.
The unassuming shrine sat in a lagoon, about 15 kilometers west of the declining Teotihuacan. “Really in the middle of nowhere,” says Sofía Pacheco-Forés, an archaeologist at Hamline University. No pyramids or palaces loomed nearby. Yet radiocarbon dates attest that for more than 300 years, between 640 C.E. and 990 C.E., people returned to the spot to carry out mass killings. Based on the location of cuts in the bones, the victims suffered throat slitting, blood draining, and finally decapitation while facedown.
To figure out what had happened here, Pacheco-Forés, then a graduate student at ASU, teamed up with Morehart. Their team analyzed the teeth and bones of 73 victims, measuring strontium and oxygen isotope ratios. Those can reveal where a person was born and where they traveled throughout their life.
The data indicate roughly 70% of the sacrificial victims were immigrants or foreigners, the researchers report in a forthcoming issue of the Journal of Anthropological Archaeology. The individuals spent their early years in diverse regions of Mesoamerica, based on the isotopes in their first molars, which solidify by age 3. Meanwhile, their third molars, formed between ages 7 and 12, and bones, which incorporate isotopes throughout life, suggest they later moved to the highland basin that cradled Teotihuacan and neighboring hamlets. Some of the victims likely lived there for decades. Though most were adult men, at least 28 of the 180 total sacrifices were teens or grown women. So they probably were not captured soldiers.
Previous isotope studies have shown roughly one-third of Teotihuacan city residents were immigrants. If the post-Teotihuacan population had a similar makeup, finding more than two-thirds migrants at the shrine suggests outsiders were targeted for sacrifice. Who did the killing—and why—remains unclear because no accompanying settlement or homes have been found.
The researchers suspect ordinary locals were responsible. According to Pacheco-Forés, the downfall of a powerful center like Teotihuacan—which likely happened several decades before the sacrifices began—may have bred mistrust and violence against outsiders. The sacrifices could still have been religious in nature—tributes to deities—but the choice of immigrant victims may have been driven by social anxieties.
Still, some experts are skeptical that foreigners were singled out for sacrifice. No one has looked at the isotopic makeup of nonsacrificial burials from this time and place, Clayton notes. So it’s possible foreigners simply comprised a sizable segment of the population, even larger than during Teotihuacan’s heyday.
It doesn’t make sense to compare this site with the general population of Teotihuacan or its largest killing events orchestrated by top rulers, adds archaeologist Linda Manzanilla of the National Autonomous University of Mexico, University City. She says a better comparison is a smaller sacrifice within a residential neighborhood of Teotihuacan, probably led by upper-class residents around 350 C.E. There, she found nearly the same proportion of migrants as was found at the new shrine site.
What’s more, isotopic differences may not align with past people’s identities and ethnic categories, cautions Nawa Sugiyama, an anthropologist at the University of California, Riverside. “How you interpret the [results] is very much contingent on how we define what local means and what foreigner means.”