A decade ago, a large, jumbled mass of human remains was found in a cave in Frontera Comalapa, a town in the southern state of Chiapas, Mexico, near the Guatemalan border. Given the state’s struggles with drug cartels, violent infighting, and reported human trafficking and forced prostitution, authorities opened up an investigation into the apparent gruesome crime.
The results are finally in—and it turns out the cave wasn’t actually a crime scene. Instead, the 150 skulls found there in 2012 are pre-Hispanic, dating to between 900 and 1200 C.E., according to a statement from Mexico’s National Institute of Anthropology and History (INAH).
Archaeologists theorize that the Frontera Comalapa remains belong to victims of ritual decapitation whose skulls were placed on “a kind of trophy rack” known as a tzompantli, reports the Associated Press (AP). The practice was common in Aztec, Maya and other Mesoamerican civilizations.
As Dolly Stolze explained for Atlas Obscura in 2015, the word tzompantli translates to “skull rack,” “wall of skulls” or “skull banner.”
“Like a giant abacus constructed with human heads instead of beads, the Aztec tzompantli were constructed with wooden beams with skulls skewered in rows on horizontal poles,” Stolze wrote. “The skulls displayed on these racks were harvested from victims of human sacrifice or from soldiers who died on the battlefield.”
Researchers put the total number of bodies found in the Frontera Comalapa cave at around 150; some bones are so fragmented that an exact calculation is difficult. More women than men seem to be represented in the remains, and the skulls include those of three infants, says Javier Montes de Paz, an anthropologist for the INAH’s Chiapas Center, in the statement.
The team based its conclusion on a few key findings. Though anthropologists discovered bone fragments other than skulls at the site, including pieces from arms and legs, they have not yet located any intact bodies. This is consistent with decapitation rather than a mass grave. In 2012, the Chiapas Attorney General’s Office also uncovered remnants of aligned wooden rods at the site—the remains of what archaeologists believe was a structure on which the skulls could be displayed.
“Many of these structures were made with wood, a material that disappeared with time and could collapse all the skulls,” says Montes de Paz in a separate filmed statement.
Written evidence corroborates anthropologists’ accounts of these sacrificial rituals. When Spanish explorers arrived in what is now Mexico, they were struck by the gruesome displays.
Soldier and chronicler Andrés de Tapia arrived at the Aztec capital of Tenochtitlan in 1519 and was impressed and horrified by one such tower. Per El Economista’s J. Francisco De Anda Corral, he described a tower decorated with “many heads of the dead. … [F]rom top to bottom there were as many men on the [tower’s] posts as could fit, and on each post there were five heads of the dead strung by their temples.”
As anthropologist Jack McIver Weatherford noted in a 1985 monograph, Tapia counted 136,000 skulls in that tower alone.
Experts are still studying the site that terrified Tapia. As Hollie Silverman reported for CNN in 2020, archaeologists unearthed a tower of more than 600 skulls while excavating Huey Tzompantli, in the heart of what is now Mexico City. Many of the skulls have perforations thought to have been made so they could be easily hung at the ritual sacrifice site.
Unlike skulls discovered at other sites, the Frontera Comalapa bones don’t contain holes. According to the AP, experts say that they “may have rested atop poles, rather than being strung on them.”
The skulls are also missing all their teeth. Experts don’t necessarily find that surprising: Per the statement, human remains recovered from two other cave sites in Chiapas in the last 40 years were similarly toothless.
Chiapas is full of caves, many of which contain pre-Hispanic artifacts and signs of ritual use in years gone by. Some even contain large numbers of skulls: In the 1980s, researchers found 124 skulls in the Cueva de las Banquetas, and in 1993, a Mexican and French team discovered five skulls placed on a wooden grid in the Cueva Tapesco del Diablo.