Archaeologists last year described it as the largest known mass child sacrifice anywhere in the world: 140 children and 200 llamas slaughtered around AD 1450 on a bluff overlooking the Pacific Ocean in the Chimu state—what is now northern Peru. At the time, archaeologists had a theory about why the children were killed, and a new study in PLOS One is again pushing the theory. The results of the excavation and study of the remains indicate El Niño might have been to blame. "A thick layer of mud on top of the sand" the children were buried in; that some children were deposited atop the wet mud; footprints made in the mud by children and adults; and evidence llamas were dragged in the mud provide clues as to possible motivation.
The area is otherwise a desert, so that mud layer suggests the sacrifice came after heavy rain or flooding, in an area "that receives negligible rainfall under normal conditions"—just a tenth of an inch a year, reports the Washington Post. The New York Times says the results of such precipitation would have been severe, "flooding crops, killing fish, and sweeping people away." The weather and the sacrifice could just be a coincidence, but the paper notes it's "tempting to hypothesize that the two events are associated" and that they were trying to curry the gods' favor. "The sacrifice of such a large number of children and camelids constituted a significant investment of resources for the Chimú state," notes the study. (Read more on the grisly sacrifice here.)