Margen
One of the oldest operations we know of involved opening a hole in the skull of a living person. It's called trepanation, and it was already practiced thousands of years ago, long before anesthesia.
The astonishing part is that many patients survived. We know this because in numerous ancient skulls the edge of the hole appears rounded and regrown: the bone kept growing afterward, a sign that the person lived for months or years after the procedure.
Why it was done isn't known for certain: perhaps to treat blows to the head, headaches or, according to some theories, for ritual reasons. Either way, it shows that surgery is far older than we tend to imagine.
Source: Smithsonian Magazine