Trepanning AKA Trepanation, AKA Trephination
Imagine someone taking a really sharp rock and cutting your scalp, then flopping your scalp open like a wet rug and using a – probably – different rock to saw into your skull. They then make a roughly rectangular shape, pop out part of your skull bones, put your scalp back, and send you on your way.
This is the ancient art of trepanation.
Sometimes the hole would be more square, sometimes four cuts are made and sometimes five, depending on the method, and sometimes a round gouging tool would be used that produced round holes instead of square. But believe me when I tell you that this skull-hole-cutting thing was the hot body modification trend of the Neolithic Period, aka the Late Stone Age.
We know this because at some sites, like one in France from 6500 BCE, up to a third of all the skulls were trepanned. Around 5-10% of all the skulls ever found from the Neolithic have at least one hole in them. Some have two. And when I say all the skulls, I mean all the skulls from everywhere. People in China were doing it. People in the Americas were doing it.