Archaeologists in Peru have found remains of more than 140 children who were sacrificed around 550 years ago as part of a ritual, National Geographic reported on Thursday. This could be the biggest-ever mass sacrifice of children in world history, according to the evidence.

The children were sacrificed with 200 llamas on top of a cliff on Peru’s northern coast in a region that was ruled by the Chimu Empire until around 1475. The cliff is located near Trujillo, Peru’s third largest city.

Human sacrifice has been recorded in the Aztec, Maya and Inca empires but “the discovery of a large-scale child sacrifice event in the little-known pre-Columbian Chimu civilisation is unprecedented in the Americas – if not in the entire world”, National Geographic said.

“I, for one, never expected it,” physical anthropologist John Verano, one of the researchers, told the magazine. “And I do not think anyone else would have, either.”

The first remains were discovered in 2011, when an international team led by John Verano and Peruvian explorer Gabriel Prieto began the excavations. Initially, they found remains of 42 children and 76 llamas at a 3,500-year-old temple. In the next five years, they found more, and also recovered ropes and textiles dating back to the first half of the 15th century.

“The skeletal remains of both children and animals show evidence of cuts to the sternum as well as rib dislocations, which suggest that the victims’ chests were cut open and pulled apart, perhaps to facilitate the removal of the heart,” the magazine said.

The children were between five and 14 years old and were buried facing the Pacific on the west, the researchers said. The llamas were less than 18 months and were buried facing the Andes mountains on the east.