Around 1450 C.E. on the northern coast of Peru, more than 140 children and 200 young llamas were marched to their deaths. It’s one of the largest known sacrifices of children in history, the Los Angeles Times reports. The site, called Huanchaquito-Las Llamas, was part of the Chimú Empire, and the chemical isotopes preserved in the children’s bones suggest they came from all over Chimú territory, National Geographic adds. Normally the region is very dry, and the Chimú relied on complex irrigation systems to grow enough food. But the sacrificed children, boys and girls ranging from 6 to 14 years old, were buried in a thick layer of mud, suggesting that at the time they were killed, an El Niño event was causing heavy rains and catastrophic floods. The sacrifice might have been performed in an attempt to stop the rain.