An Aztec tower of skulls near the Templo Mayor includes women and children's crania, casting doubt on the conventional view that it's only captured enemy warriors who get sacrificed:
https://www.theguardian.com/world/2017/jul/01/tower-human-skulls-mexico-city-aztec-sacrifices
Looks like they were smashed on both sides - to allow a pole through?
While the structure may have contained the concatenated crania from human sacrifices, there is another possibility: the occipital remains of slaughtered rebels (https://en.wikipedia.org/wiki/Skull_Tower) (and their dependents).