In the fifteenth-century Andes, surgeons sometimes opened the skull of a living patient. They could scrape away bone gradually, cut a circular groove or remove a section of skull. Archaeologists call this operation trepanation. Many patients survived: a large study of ancient Peruvian skulls found evidence of recovery in an estimated 75% to 83% of Inca-period cases.
The surgeons worked without antibiotics, modern antiseptic methods or medical imaging. A blow to the head, perhaps received in battle, seems to explain some operations. Other skulls bear openings but no visible fracture, leaving the reason for treatment unknown. The bone records where a surgeon cut and whether the opening began to heal. It cannot reveal the patient’s symptoms, the practitioner’s advice or the arrangements for treatment.
The often-repeated 80% figure comes from particular Inca-period archaeological samples, and cannot describe the success of skull surgery throughout the ancient world. Earlier communities in Peru had lower estimated survival, and the results of different regional groups could diverge considerably. These operations took place over centuries, as techniques and survival prospects appear to have changed.
What the 80% Survival Rate Actually Measures
David S. Kushner, John W. Verano and Anne R. Titelbaum compared survival estimates in a 2018 study in World Neurosurgery. Their analysis drew on research involving more than 800 trepanned skulls from several Peruvian regions and periods. For approximately 400–200 BCE, they estimated long-term survival at about 40%. A later series, dated AD 1000–1400, averaged about 53%, with substantial variation between groups. The Inca-period figures, from the fifteenth century onwards, reached approximately 75%–83%.
The percentages come from archaeological assessments, since no ancient medical records give these figures. Removing bone leaves sharp edges around an opening in the skull. If the patient remains alive, the bone may begin to remodel: the cut surfaces become smoother and new bone can appear at the margins. Clear healing shows that a person lived after the opening was made. An unhealed cut may indicate death during or shortly after an operation, although a cut made after death or other circumstances can leave a similar appearance.
One pre-Inca subset in the study produced a figure of 91%, but it contained only nine skulls. Nine examples cannot establish survival rates for a wider population. The broader Inca-period material yields the 75%–83% range, still subject to the limits of archaeological sampling. Even here, researchers distinguish survival shortly after treatment from the longer period suggested by extensive bone repair.
Another dataset comes from a 2008 study of the Cuzco region by Valerie Andrushko and John Verano examined burials at 11 sites, identifying 66 people with a total of 109 trepanation openings. The researchers estimated overall survival at 83%. Some individuals had more than one opening, so the count of openings exceeds the count of patients. The findings describe Cuzco rather than the full range of Peruvian communities.
An 80% estimate does not mean four out of five people who sought surgery recovered their health. People without surviving remains never enter the analysis, and archaeological collections may favour certain burial groups, places or centuries. A healed opening also establishes neither relief from pain nor a return to ordinary life. Healing establishes survival after an intervention, but reveals much less about the patient’s later health.
How Ancient Peruvian Surgeons Opened the Skull
Opening the skull had a long history in Peru before the Incas expanded through the Andes in the fifteenth century. Communities along the southern coast had already practised trepanation for centuries. Surgical methods differed among communities. Archaeologists can recognize scraping, circular grooving, drilled or bored holes, and straight cuts by examining tool marks on surviving skulls. The choice affected both the shape of the opening and the danger faced by the patient.
Scraping gradually wore through the outer skull and the softer, spongy bone beneath it. In circular grooving, the operator deepened a cut around a selected area until the central piece could be lifted out. Some practitioners bored several holes and connected them; others used straight incisions to remove a section. Every approach risked cutting beyond the bone. Beneath it lay blood vessels and the dura mater, the tough membrane covering the brain, which an uncontrolled instrument could injure.
The Cuzco study found a preference for scraping and circular cutting. Openings were frequently placed away from especially hazardous anatomical areas, and in some later examples the cuts were smaller and more closely controlled. These features suggest that practitioners understood differences in skull thickness and the risks of cutting too deeply. They do not tell us how that knowledge was taught or whether all surgeons received similar training.
Improvements were uneven across the Andes. Danielle Kurin’s 2013 research studied 45 trepanations on 32 individuals from five Andahuaylas sites, approximately AD 1000–1250. Several approaches were used at once. Scraping produced the most evidence of healing in that sample; grooving, drilling and straight cuts were associated with poorer outcomes. Those outcomes cannot be generalized to every Andean community or century.
An opening’s position, the underlying injury, the skill of the practitioner and the conditions of treatment could all affect a patient’s chance of recovery. Surviving bones cannot measure the contribution of each factor. They do establish that people in several Andean populations survived deliberate removal of cranial bone, and that some later collections show much more frequent healing.
Why Would Someone Undergo Trepanation?
Skull injuries provide the clearest explanation for many operations. Andean combatants used clubs, slingstones and other weapons that could break the skull. A depressed fracture pushes bone inwards, potentially injuring the tissues below. Removing fragments or opening the skull may have been intended to address such damage. Archaeologists cannot determine from a healed skull whether an operation relieved dangerous internal pressure in that particular patient.
Some individual skulls preserve more direct evidence. Museo Larco’s display of trepanned skulls includes an adult man whose face and head bear healed injuries alongside a trepanation in the right parietal bone, also showing regeneration. Museum specialists consider the fractures compatible with blows from weapons. The combination of healed trauma and a surgical opening supports a connection with violence in this case, without making warfare the explanation for every trepanation.
Another example comes from the National Museum of Archaeology, Anthropology and History of Peru. A Paracas-period skull has a trepanation over an injury apparently inflicted with a star-shaped club. The museum identifies the opening as scraped and records a sheet of gold associated with the skull. It expressly states that nothing shows the gold was worn over the surgical wound during life. The presence of a gold sheet beside the skull does not establish its use as a surgical covering.
Other skulls show surgical openings with no visible fracture. Persistent pain, the effects of an earlier blow, or illnesses that left no trace on bone could have led to an operation. Headaches and seizures are possible explanations often raised by researchers, although neither can normally be diagnosed from an ancient skull. Religious meanings may also have accompanied treatment. Religious explanations remain possible in particular cases, but there is no basis for treating the release of evil spirits as the purpose of every operation.
The distribution of patients also remains uncertain. Kurin found trepanations among adults in the Andahuaylas sample, predominantly men, but none among the examined children or individuals with cranial modification. Those observations describe that particular collection, not a rule governing the whole Andes. They nevertheless suggest access may have differed between social groups. The skulls record who was treated in that sample, although they cannot explain how practitioners selected patients.
What Tools and Preparations Can Be Identified?
The cutting tools available in Peru included both stone and metal. Obsidian, a volcanic glass, breaks into exceptionally sharp edges; copper and copper-alloy knives are also known from archaeological and museum collections. Museo Larco records associate obsidian and metal blades with trepanation. A knife found near a skull cannot be identified as surgical merely from its burial context. Elaborately decorated ceremonial blades could have served other purposes.
The curved Andean knife called a tumi is often pictured in accounts of Inca surgery. It belongs among the possible cutting tools, though an image of the blade does not identify what any specific practitioner used. Demonstrating that connection would require comparing the cuts in a particular skull with plausible instruments. Most surviving operations cannot be matched securely to a particular blade.
Some remains also suggest how treatment was prepared and completed. The Andahuaylas research discusses possible hair removal, the use of poultices and coverings or repairs placed over openings. Those suggestions come from individual finds, not evidence for a standard procedure across Peru. Kurin also identified cuts made after death, perhaps connected with learning or experimentation. An opening in a skull therefore need not have been made while its owner was alive.
Evidence for pain relief is scarcer. Andean people knew coca and other plants, and alcoholic drinks may have helped patients endure treatment. No evidence identifies an anaesthetic, preparation or dose administered to a specific person whose skull survives. Claims that coca paste reliably numbed the scalp, or that Inca surgeons possessed an equivalent of modern anaesthesia, go beyond the record. Cutting the sensitive scalp without effective pain relief would have caused severe pain.
Cutting through bone was only one danger. The scalp wound had to close, and bleeding or infection could still kill someone after a technically careful operation. Healing shows that at least some patients lived through a period in which their injuries required care. The smooth edges of their skulls cannot reconstruct dressings, sanitation or nursing routines. The suggestion that operations performed outdoors with obsidian were naturally sterile is also unsupported.
How Bone Healing Reveals Survival, and Its Limits
Bone continues to change after it is injured. Cells remove damaged tissue and lay down new material, potentially rounding and beveling the edges of an opening made during life. Researchers examine these margins under magnification, sometimes using X-rays or computed tomography. Cut directions, surface features and the surrounding bone help them decide whether they are looking at deliberate surgery, damage from an accident or another kind of lesion.
A 2020 study in the Journal of Anatomy by Caroline Partiot and colleagues compared 90 archaeological skulls with scans of 14 living-era patients who had received cranial surgery. The comparison supported the interpretation of smooth, rounded margins as evidence of remodelling. The shape of a healed margin, however, could not establish exactly how long a patient lived afterwards. Calling an ancient opening healed does not establish that its owner lived for decades afterwards.
Another diagnostic problem is pseudotrepanation. Some diseases or naturally occurring defects produce openings resembling those made by a tool, especially in damaged ancient bones. Archaeologists must examine the cut surface, overall shape, other injuries and evidence of repair together. An opening without healing is uncertain too: the patient may have died shortly after surgery, or the cutting could have happened after death. The distinction between surgery, natural defects and post-mortem cuts affects every survival estimate.
An apparently healthy skull may conceal an infection elsewhere in the wound. Sometimes it changes the bone, leaving recognizable lesions. In other cases a dangerous infection of the soft tissue leaves no trace on the skeleton. A trepanation surrounded by apparently healthy bone therefore does not prove that surgical instruments, hands or the wound were sterile.
A number of people underwent more than one trepanation. Their skulls carry separate openings, sometimes with different amounts of healing, showing that at least some survived repeated interventions over time. The sequence does not reveal whether further surgery treated new injuries, recurring symptoms or complications of an earlier operation. An opening that healed also tells us nothing by itself about the eventual cause of death or how old the person became.
Trepanation Beyond Peru
Trepanation has been identified in many regions outside the Andes, including ancient and prehistoric Europe and western Asia. Peru has yielded an unusually large body of studied examples, although trepanation was practised elsewhere and its place of origin is unknown. The same practice appearing across continents does not establish a common inventor or a route along which the technique spread. Different communities may have reached similar solutions to comparable problems independently.
A Bronze Age skull from Jericho in the southern Levant, dated about 2200–2000 BCE, carries four trepanation openings. The Science Museum Group’s object record describes them as healed; a Wellcome photographic record more specifically reports three holes at different stages of healing. At least some interventions were survived. The disagreement in descriptions means that a claim of four separately proven successful surgeries would give the evidence more certainty than it has.
The well-known skull from Neolithic Ensisheim, in Alsace in eastern France, is often discussed as a case of two trepanations. Its interpretation has nevertheless been contested. A 1998 discussion in Nature questioned the claim that it was the earliest unequivocal example, and a 2022 regional review recommended examining the markings again. It is an important specimen in the history of the research, but neither an uncontested first nor the basis for a complete account of an individual operation.
The Jericho and Ensisheim specimens show that trepanation was practised far beyond Peru. Their statistics cannot simply be compared with Peru’s, because excavation, sample selection, dating and the criteria used to diagnose surgery differ. Peru offers numerous sizeable collections spanning successive centuries, allowing regional and chronological comparisons when sampling differences are taken into account.
Did Inca Surgeons Outperform American Civil War Doctors?
The 2018 study also compared ancient Peru with head surgery during the American Civil War of 1861–1865. It reported mortality estimates of approximately 46%–56% in the nineteenth-century cases, whereas signs of survival appeared in around 75%–83% of the Inca-period series. These are the figures reported by the study’s authors, and they reflect the very different risks faced by the patients in each setting.
The treatment circumstances were markedly different. Civil War surgeons faced severe gunshot injuries, sometimes after long delays, in crowded hospitals where infections were common. Archaeologists usually cannot determine the initial injury, other medical conditions or treatment setting for the Peruvian skulls. The 2018 authors themselves noted that short- and long-term survival could not be measured in the same fashion for the Civil War cases and the ancient material.
The figures demonstrate survival after many Inca-period operations, but cannot show how an Andean surgeon would have handled a Civil War gunshot wound. The gap between the rates has no demonstrable single cause. Less severe injuries, selective treatment, avoidance of risky parts of the skull, established surgical skill and differences in infection risk might all have contributed. The evidence cannot apportion those possibilities.
Surgery continued to change after the Civil War. Anaesthesia, antiseptic methods, aseptic procedures and better diagnosis improved practice during the late nineteenth and early twentieth centuries, before modern cranial surgery emerged as a specialized discipline. The Peruvian skulls document considerable surgical skill, without implying that ancient practitioners possessed the techniques of modern neurosurgery.
What the Trepanned Skulls Still Cannot Tell Us
Repeatedly making openings in living skulls required control of tools and practical familiarity with a dangerous part of the body. The healed wounds, the careful placement of cuts and the stronger results associated with certain methods point towards practitioners learning from experience and continuing skilled traditions. The skulls preserve no names or occupational labels for those who performed the operations.
The surviving evidence leaves questions about the patients themselves. We cannot know how consent was obtained, how a young practitioner learned, whether a treated person returned to ordinary work or how often a community refused the operation. Gender, rank and access to care may have affected the distribution of trepanations, but the evidence must come from particular populations and burials. A trepanation cannot, on its own, establish either high social status or special religious esteem.
For centuries, Andean people deliberately cut through the skull, and many of those who underwent the procedure survived. In some communities, later skulls show substantially more evidence of healing. The bone retains the physical consequences of interventions carried out by people whose names and methods were rarely recorded. Those healed margins preserve evidence of practical skill while leaving the patients’ experiences largely unknown.
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