Here’s an image of some trepanned skulls taken in Lima, Peru. Trepanation or trepanning refers to the deliberate drilling of a hole into a human skull, practiced for many years in various pre-Columbian cultures in Mesoamerica. One purpose for trepanation was to treat medical ailments. A knee-jerk reaction to seeing a skull with a hole drilled into it is probably to think medical practitioners at the time didn’t know what they were doing.
Surprisingly, however, trepanation was a sophisticated surgical procedure used to treat head injuries often arising from combat. The purpose was to relieve pressure due to fluid build-up after head trauma, and trepanation techniques were even standardized and perfected. By the 1400s, survival rates were closing in on 90%. This wasn’t just someone striking a blow on a patient’s head, repeating the wound he already got on the battlefield, but it was a skilled surgeon going to work. And this sounds reasonable given that the procedure was practiced and refined for over a thousand years.