When you imagine ancient surgeons, you may wince thinking about the primitive techniques. However, it turns out that Incan surgeons were quite skilled. Judging from remains found in Peru from as far back as 1000 AD, researchers found that surgical techniques were standardized and continually improved upon.
One procedure, known as "trepanation," involved removing part of the skull to treat head injuries. While it may sound counterproductive, it worked. Or it eventually did. Skulls from around 1000 AD show little signs of bone healing, which means that the patient likely died after the procedure. However, by the 1400s, the fatality rate was down to just 10%.