In 2012, authorities in the southern Mexican state of Chiapas entered a dark cave and confronted a horrific site: About 150 skulls lay sprawled on the ground, all with missing teeth and shattered bits of bone.
Police launched an investigation, assuming it was a crime scene of migrants murdered near the Guatemalan border, where gang violence is a common occurrence.
It was indeed a crime scene. Just not one that has happened recently.
Last week, 10 years after the discovery, authorities said in a statement they had determined the skulls came from sacrificial murders between AD 900 and 1200.
“We’ve already received a lot of information,” Javier Montes de Paz, an archaeologist who analyzed the bones, said at a news conference on April 11. “But it’s also important to note: What were those skulls doing in that cave?”
Researchers at the National Institute of Anthropology and History analyzed traces on the bones and determined that the deaths had occurred centuries ago. Such signs would not appear until “much, much time” had passed, Mr Montes de Paz said.
The researchers found that the victims had been decapitated, most of the bones belonged to female victims and all were missing teeth, although it was unclear whether they had been extracted before or after death, Mr Montes de Paz said.
The researchers also found the skeletal remains of three babies.
The pre-Hispanic bone stack in Comalapa Cave was likely a tzompantli — an altar to worshiping gods that would look like a modern trophy rack, with skulls on aligned wooden sticks, Mr. Montes de Paz said. Similar practices were common in Maya, Aztec and other Mesoamerican civilizations, according to Smithsonian Magazine.
The wooden material “disappeared over time and could have caused the skulls to collapse,” added Mr Montes de Paz.
Researchers in the cave also found aligned wooden sticks, another sign of a tzompantli, according to a statement from the National Institute of Anthropology and History.
Although the researchers have not yet completed their investigation, Mr. Montes de Paz said it is highly likely that several Mesoamerican communities have used the cave. The two entrances were so steep that researchers had to use a ladder to get in.
It was unclear how the skulls were found ten years ago, and by whom. Authorities said in a statement that a “complaint” had warned them about the discovery in the town of Carrizal, in the municipality of Frontera Comalapa. The National Institute of Anthropology and History did not respond to questions by email on Wednesday.
Anthropologists studying the skulls found other bone fragments at the site, including a femur and pieces of arms. However, no intact bodies had been found, Mr Montes de Paz said.
The Spanish invasion took place in the 1500s. According to Smithsonian Magazine, the Spaniards were afraid of the rituals when they arrived.
But the sacrifices seemed to have been common in Chiapas. The National Institute of Anthropology and History said that in the 1980s, anthropologists explored Cueva de las Banquetas, a cave, and found 124 skulls without teeth. In 1993, Mexican and French explorers in Ocozocoautla traveled to Cueva Tapesco del Diablo, another cave with five skulls inside.
Mr. Montes de Paz said his team would like to further explore Comalapa Cave soon.
In the future, if people visit such sites and see skulls, they should not touch or pick up anything, he said. Otherwise they could affect the archaeological integrity of the site. The people who found the skulls in Chiapas in 2012 accidentally touched some bones, he said. “You influence history,” he said. “And a lot of information is lost.”
Still, he believed that after more analysis, the skulls’ story could soon be fully told.