Back in 2012, police in Mexico were stunned when they discovered an "altar of skulls" resembling a crime scene inside a cave near the Guatemalan border.

Police weren't immediately clear on what they had discovered. As the nearby town of Frontera Comalapa is reportedly notorious for "violence and immigrant trafficking," authorities initially believed the discovery to be from a recent incident.

Thinking that they had stumbled upon a modern-day, gruesome killing site, authorities were recently (somewhat) relieved to learn that the 150 skulls were actually from victims of ritual decapitation, and were more than 1,000 years old.

According to HuffPost, the National Institute of Anthropology and History spent a decade researching and analyzing the bones, which are now said to be pre-historic, dating from around 900 to 1200 AD.

According to the research, most of the skulls found belong to adult female victims sacrificed during ancient rituals.

Experts identified the skulls and shared that their placement in the cave was a key indicator confirming that they were part of a centuries-old indigenous ritual site involving ancient sacrifices.

Historical experts say the discovered skulls were showcased on a "tzompantli," which is described as a pre-historic trophy rack commonly found in ceremonial plazas to showcase the sacrificed dead.

According to archaeologist Javier Montes de Paz, there is a strong need to continue more archaeological research in the area where the cave of skulls was found. If residents uncover sites of interest, they are urged to contact both local authorities and archeologists.

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