When Mexican authorities were alerted to a cave full of human skulls 10 years ago, they thought they had discovered the site of a gruesome modern murder scene. Now, new research suggests that these skulls may actually be the result of ritual human sacrifices around 1,000 years ago, in which people were decapitated and the heads put on a trophy rack within the cave.  

“Believing they were looking at a crime scene, investigators collected the bones and started examining them in [state capita] Tuxtla Gutierrez,” said Mexico's Instituto Nacional de Antropología e Historia (INAH) in a statement.

“We still do not have the exact calculation of how many there are, since some are very fragmented, but so far we can talk about approximately 150 skulls,” said physical anthropologist Javier Montes de Paz during a virtual conference on the preliminary findings.

While you may wonder how an archaeological site got confused with a modern crime scene, it was not immediately apparent owing to the fact that the skulls deviated from expected findings from that time period. Skulls from pre-Hispanic Indigenous cultures are often “bashed-in” and left in ceremonial circles, while these were entirely intact and left in a cave in Frontera Comalapa, in the municipality of Chiapas in southern Mexico. Such conditions would be ideal for violent gangs in the area – which are known for human trafficking, according to AP – to dump human remains. 

However, genetic analysis of the bones suggests these are much older. Alongside the skulls, there were a few other human bones, including tibias, though not a single complete burial was discovered. Each skull had the teeth removed, consistent with practices of the time, and the presence of wooden sticks suggests that the skulls were placed on a funerary “alter of skulls”, known as a tzompantli. These scaffold-like constructions were used by Mesoamerican civilizations to display the skulls of captives or sacrifices, with one found to contain 650 skulls in a massive complex.  

"Many of these structures were made of wood, a material that disappeared over time and could have collapsed all the skulls," Montes de Paz continued. 

Based on modifications of the skull, it is thought the remains date from 900 – 1200 CE. During this time, it was believed that human sacrifice would please the gods and contribute to the continued success of the Aztec people, and sacrifices could include anything from adult males and females to young children. 

"We have recognized the skeletal remains of three infants, but most of the bones are from adults and, until now, they are more from women than from men," said Montes de Paz.  

Archaeological work will now continue in the area to illuminate more of the incredible find, and the researchers appeal to the public to contact INAH if they stumble across any more remains in the Frontera Comalapa area.