Some 2,000 years ago, a Peruvian surgeon picked up a simple tool and began to scrape a hole in the skull of a living human being. Before the surgery was over, much of the patient’s fractured upper skull had been removed without the aid of modern anesthesia or sterile techniques.

The patient, almost incredibly, survived.

The ghoulish operation is only one example of trepanation, an ancient medical practice that has been freshly examined in Holes in the Head: The Art and Archaeology of Trepanation in Ancient Peru, a new book by physical anthropologist John Verano of Tulane University and five collaborators.

Thousands of years ago, surgeons trepanned patients in early Europe and the South Pacific, and trepanation was still being practiced in East Africa as recently as the 1990s. But the procedure reached its apex in Peru between the 14th and 16th centuries A.D.—at least judging by the number of trepanned skulls found in the region and the high survival rates conveyed by signs of healing in the bone.

Verano spoke with National Geographic about his views on the art and science of trepanning, based on decades of study and more than 800 trepanned skulls.

How common was trepanation in ancient Peru?

It was surprisingly widespread. In its heyday, it basically covered what was the territory of the Inca Empire, which was at that time the largest empire in the world geographically. [Trepanation] was not just something here and there. It was all over. [Peru] has more skulls with trepanations than everywhere else in the world combined.

Why was trepanation so prevalent in Peru?

The weapons they used in war were primarily sling stones and bashing clubs, things that would cause fractures to the head, whereas in many other parts of the world, the weapons were bows and arrows or swords or spears. Those things don't cause the frequency of head wounds that bashing weapons and sling stones do.

Why did Peruvian surgeons turn to such a dramatic procedure?

It probably started as a very simple thing—cleaning the scalp after a blow to the head and doing some simple things like picking out broken pieces of bone, which would be dead. They learned early on that this was a treatment that could save lives. We have overwhelming evidence that trepanation was not done to increase consciousness or as a purely ritual activity but is linked to patients with severe head injury, [especially] skull fracture.

Were you surprised by the survival rate of Peruvian trepanations?

I didn’t realize when I began that the Inca rates would be so high, that they would push over 70 percent. The very earliest trepanations [were] from Paracas, from the south coast of Peru. [There was] only about 40 percent survival, but when you looked at the size of the holes they put in the head—and I still don’t know why they opened such huge windows into the skull—there are a fair number that survived. I’ve been able to put to rest the idea that Paracas was some odd, irrational experiment by shamans.

View Images A tool used for trepanation around 11 to 6 B.C. Photograph by Markus Matzel, ullstein bild, Getty

Why were the Peruvian practitioners so successful compared to Western attempts?

[In the West,] doctors would just rinse [surgical tools] off in water and wipe them down and use them in another patient. Also, surgery was done in hospitals. That’s where many people get infections even under the best circumstances today. In Peru they didn’t have hospitals. People were probably operated on in open-air situations and probably with tools that were not used over and over again. So the risk of infection was probably a lot lower.

Wouldn’t such surgery have been hideously painful?

There are a lot of nerves in your scalp. If you tried taking a knife or a razor blade to your scalp, it would hurt, but you could grit your teeth and deal with that. But the bone itself has very few nerves. So if a doctor told you, “We’re going to scrape through your skull and it’s not going to hurt,” he or she would be telling you the truth.

Can modern medicine learn anything from the ancients?

We won’t gain anything in terms of surgical technique, because tools have changed a lot. In part, my goal [in writing the book] is to educate people. We can put aside any idea that trepanation was a primitive, backward practice. It’s important to understand how things were done back then and some of the amazing feats in terms of high survival rates.