Ancient Incan societies may have asserted their power over unruly subjects by displaying the severed, mutilated heads of protestors along a rope, according to new research published in the journal Latin American Antiquity.

Archaeologists excavating Iglesia Colorada, one of Chile’s most famous Inca-style settlements, have found the modified skulls of three young females between the ages of 16 and 30 and that of a child’s tossed in an ancient rubbish pile alongside animal bones. Characteristics of the skulls, like a lack of teeth, indicate that the four individuals had a similar pathological profile, either from stress, infection, or genetic causes.

The skulls all shared another similarity: each had two circular holes bored into the frontal lobe and a third in the parietal, likely so they could be strung together in what the authors describe as “shocking and powerful displays of violence”.

Such methods of power have been observed in other ancient societies in the region. The nearby Paracas and Nasca cultures created cave art that showed mutilated bodies and they adorned pottery with people holding severed heads. In the Ica and Acarí Valleys, archaeologists have found hundreds of trophy heads with post-mortem alterations, such as enlarged parts of the skull, removed vertebrae, preserved facial soft tissues, and the mouth and eyes sewed shut.

In Chile, heads have been found inside net bags as a secondary interment following death, while there are representations of severed heads in snuffing tablets in the Atacama Desert. Dismembered heads in this part of the world served as a “powerful and iconic” symbol of victory and influence over enemies. But before now, there was no evidence that such practices occurred in the marginalized cultural found at Iglesia Colorada.

Radiocarbon dating suggests that the heads were decapitated in the village during a time of transition from Diaguita to Incan rule, suggesting the “observed pattern of severed head modification may represent new ideological efforts for controlling possible social unrest." Economic changes and political agendas may have created social stresses that they believed called for asserting dominance and control over newly acquired subjects.

The heads are now preserved at the Museo Regional de Atacama.