Young children selected to be sacrificed as part of elaborate Inca rituals were given psychedelic and intoxicating substances, possibly to relieve the terror of their imminent death or in the belief that the drugs would help them communicate with the gods.

“We cannot reconstruct the children’s emotions or determine precisely how they experienced these events,” says Dagmara Socha at the University of Warsaw, Poland. “However, we should not assume that being selected for a prestigious religious ceremony necessarily meant that the experience was not frightening or traumatic.”

The Inca kingdom dominated 4000 kilometres of the west coast of South America from the late 13th century until the Spanish conquest of the 16th century.

In a ritual known as capacocha, children and young women were sacrificed to the mountain gods. According to an account by Spanish friar Martín de Murúa, written in 1590, the capacocha ceremony was conducted to ensure there would be “no famine nor lack of fruits of the earth, nor would there be drought, nor pestilence, nor rebellion”.

Socha and her colleagues studied eight frozen, mummified children, seven of whom were girls, discovered between the 1920s and 90s at sites in Peru, Argentina and Chile. They are thought to have been aged between 6 and 14 when they died. It is thought some were killed with sharp weapons, while others were buried alive, says Socha.

The researchers analysed the mummies’ hair and nail samples to determine which psychoactive plants were given to children during the capacocha ritual.

Toxicological screening detected cocaine in all the hair samples, along with markers of alcohol and coca leaf chewing in half of the individuals. The team also identified harmine, a hallucinogenic compound found in the ceremonial drink ayahuasca, in one of the nail samples.

Socha and her colleagues suggest that the antidepressant properties of harmine could have been used to calm the children and maintain a positive mood.

Each sacrifice seemed to be associated with a unique chemical signature preserved in the child’s hair and nails. This may indicate that each child was “prepared” in a different way, perhaps to direct their sacrifice towards a specific deity.

“We are beginning to understand capacocha not simply as a single sacrificial event, but as a complex process involving extensive preparations, long journeys and different ritual practices,” says Socha.