Faint remains of a mural linger above the main altar in the newfound chamber, where the sacrificial rite is believed to have been carried out near the present-day town of Illimo, Peru (map).
"The ceremony, known as the presentation, was a ritual where naked and rope-bound prisoners were subjected to a ritual sacrifice," said Wester, who is also director of the Heinrich Brüning National Museum of Archaeology and Ethnography in the nearby city of Lambayeque (map).
As the prisoners—most likely apprehended during battle—were cut, priests and priestesses caught the spilling blood in cups, which were offered to the gods, he said.
"The prisoners of war were sacrificed to please the gods as a way to maintain social, political, and economic stability in the village," Wester said.
(Also see "Ancient Peru Torture Deaths: Sacrifices or War Crimes?")