Are you referring to the Catacombs of people who died from the black plague and cemeteries were over flowing with dead people? Cause that's very different than just killing people to their sky god for rain. https://en.wikipedia.org/wiki/Skull_Tower https://en.wikipedia.org/wiki/Tzompantli https://www.ancientpages.com/2019/03/21/ancient-cult-of-human-skulls-and-communication-with-other-world/