The mystery of skulls pierced with nails has been unveiled: researchers reveal insights into Iron Age traditions (photos included).

A recent study has shed light on the brutal practice of decapitation in the communities of ancient Iberia. However, archaeologists now note that this tradition may be far more complex than previously thought.

Researchers indicate that different communities could have had various motives, possibly related to ancestor worship as well as acts of intimidation. This insight was shared by one of the authors of the study, archaeologist Ruben de la Fuente-Seoane, as reported by Newsweek.

Scientists examined seven decapitated and nailed skulls discovered in two Iron Age settlements—Puch-Castelliar and Uliastret. Isotope analysis revealed that the skulls from Puch-Castelliar belonged to outsiders. They were nailed to the inner side of the city wall, apparently for the purpose of intimidation and maintaining discipline.

In Uliastret, these skulls were placed on the streets in the city center. Researchers believe this was a unique ritual of remembrance for the deceased. Indirectly supporting this hypothesis is the fact that some of the skulls belonged to local residents. However, they also hung the skulls of outsiders on the walls.

Ruben de la Fuente-Seoane notes that the researchers based their assumptions on the idea that outsiders were unlikely to be honored in the city. Meanwhile, the skulls of local residents were likely hung there by their relatives.

"This indicates that the selection of individuals for the decapitation ritual was more complex than initially assumed," the archaeologist stated.

As previously reported, nailing skulls to walls was not the most horrifying sight in the ancient world. For example, during the Stone Age in Europe, cannibal tribes were commonly found that intentionally hunted other people.