1) Mesoamerican warfare 
A tzompantli t͡somˈpant͡ɬi or skull rack is a type of wooden rack or palisade documented in several Mesoamerican civilizations, which was used for the public display of human skulls, typically those of war captives or other sacrificial victims. It is a scaffold-like construction of poles on which heads and skulls were placed after holes had be...