Bonanza of new dates rewrites the history of the Inca

Cusco and Choquehuanca, Peru—Fifteen years ago, University of North Carolina at Charlotte archaeologist Dennis Ogburn found himself looking at some impossible radiocarbon dates. They came from Chamical, a small site in southern Ecuador where Ogburn had found Inca ceramics and weapons, such as bone arrow points and a sling stone, but no domestic trash or any other sign people had lived there long term. He concluded the site was an Inca military outpost, constructed and briefly used during the expansion of the vast Andean empire out of its capital of Cusco, in what is now Peru.

According to the traditional chronology archaeologists had been using for more than half a century, the Inca conquered southern Ecuador between 1463 and 1471 C.E., during the reign of Emperor Pachacuti and under the military leadership of his son, Topa Inca. But when Ogburn radiocarbon dated a seed, wood, and charcoal from Chamical’s earliest layers, he found the outpost was likely built decades earlier, between 1432 and 1451.

That puzzling discovery echoed others from the opposite end of the empire. In Argentina, a handful of archaeologists had found Inca radiocarbon dates that were more than 50 years earlier than they were supposed to be. Their presentations had been met with skepticism and hostility, and their data were largely ignored.

But Ogburn thought the discrepancy was worth taking seriously. The traditional chronology of the Inca, a short-lived empire that left no written records of its own, was based on a Spanish colonial chronicle that claimed to capture earlier Inca oral histories. It asserted that the empire had existed for just 94 years from its founding until the Spanish conquest began in 1532 and met little resistance as it swept through the Andes. Adding just a few decades to the start of that compressed time frame, Ogburn realized, would mean the still-mysterious empire influenced the politics and cultures of South America for much longer than archaeologists understood—and that the people the Inca encountered had more time to react to, accommodate, or resist imperial expansion. In 2012, he published a paper in the journal Radiocarbon calling for Andean archaeologists to start to build a new Inca chronology from radiocarbon dates alone.

Now, thanks to statistical methods that are shrinking radiocarbon dating’s inherent uncertainties and an increasing number of reliable dates from sites all over the Inca empire, archaeologists are closer than ever to that goal. A critical mass of researchers is on board. At a meeting of Andean researchers at the Pontifical Catholic University of Peru last year, attendees unanimously voted to discard the traditional chronology and start again.

The challenge remains daunting, says Erik Marsh, an archaeologist and radiocarbon expert at Argentina’s National Scientific and Technical Research Council (CONICET). “We don’t have something that completely replaces [the traditional chronology] yet,” he says. But already, what he and others have learned confirms some of the empire’s most surprising claims about its sudden founding while also undermining its propaganda in crucial ways. The new dates—for both the Inca and the societies in their path—are transforming a top-down story of inevitable conquest into a bottom-up patchwork of negotiation, cooperation, and resistance. “The next few years in Inca research are going to be transformative,” says Julia Earle, an archaeologist at the University of Warsaw (UW).

When pioneering Andean archaeologist John Rowe developed the traditional Inca chronology in the 1940s, written records were the only reliable way to tell how old anything was. That limited dating efforts to cultures with deciphered scripts, such as ancient Egypt, or at least decoded calendars, such as the ancient Maya. The Inca, like other Andean cultures, did not use writing at all; instead, bureaucrats kept track of the empire’s inner workings with khipus, series of knotted strings that recorded numbers and likely a wide range of other information.

It’s possible an Inca historical calendar remains undeciphered in the more than 1000 khipus currently known from sites across the Andes. But Terence D’Altroy, an archaeologist at Columbia University and one of the researchers who first found early Inca dates in Argentina, thinks it’s unlikely. The Inca kept track of monthly lunar cycles, annual agricultural cycles, and the sequence of rulers, he explains, but they didn’t combine that information into linear, chronological history. There was no need, because for the Inca, the past wasn’t fixed. By interacting with—and sometimes destroying—the material of the past, such as ancient stone monoliths, the ruins of past societies, and ancestral mummies, the Inca could alter their history to better suit the politics of the present.

For example, when the last Inca Emperor Atahualpa defeated his brother Huascar in a civil war for the throne in 1532, just months before being captured by conquistador Francisco Pizarro, his troops burned the mummy of their shared grandfather, Topa Inca. Atahualpa intended to erase Topa Inca from imperial history and destroy the power of his kin group, which supported Huascar’s claim. “With a new emperor, there was always a new story,” says Dominika Sieczkowska-Jacyna, a radiocarbon expert at UW and the Silesian University of Technology.

That malleability confused colonial chroniclers who recorded Inca oral histories in the 16th century. Rowe deemed the most reliable to be Miguel Cabello de Balboa, one of the few chroniclers to assign dates to the reigns of Inca emperors. Whereas other colonial sources charted a gradual expansion of Inca power over several centuries, Cabello de Balboa, a 16th century Spanish priest, claimed the empire began abruptly in 1438, when Pachacuti deposed his father and ascended to the throne.

Cabello de Balboa’s account underpinned Rowe’s traditional chronology. It describes how Pachacuti quickly took control of the Cusco heartland and territories stretching south to Lake Titicaca, then sent three of his sons, including Topa Inca, to conquer the north, including the region around Chamical. Next, Topa Inca incorporated southern territories in Argentina, Bolivia, and Chile during his own reign, from 1471 to ’93. His successor Huayna Capac would add comparatively little land between 1493 and 1525, when power passed to Huascar, whose imperial ambitions were derailed by civil war.

“We have, of course, no way of knowing where Cabello got these dates,” Rowe wrote in a 1945 American Antiquity paper outlining his Inca chronology. But he considered the compressed timespan “reasonable” and congruent with how shallow—and, therefore, short-lived—Inca archaeological deposits tended to be.

The year after Rowe’s paper, physical chemist Willard Libby proposed directly dating wood, bone, and other organic artifacts by measuring their carbon-14, a radioactive isotope that is taken up by living things from the atmosphere and slowly decays after death. But the technique seemed unpromising for Inca artifacts. Aside from a few rare cases, radiocarbon dates are expressed as ranges that can span decades or even more than a century. If the empire only lasted 94 years, as Rowe argued, its entire existence could fall inside radiocarbon dating’s error bars.

Rowe remained a vocal defender of his chronology until his death in 2004. When D’Altroy presented his early dates from Argentina at a conference in 1997, Rowe stood up and said, as D’Altroy recalls, “You can’t trust the radiocarbon dates. Historical dates are more reliable, and I think you should think twice before publishing anything like this.”

Three decades later, archaeologists have managed to reduce—though not eliminate—radiocarbon dating’s uncertainties. Advanced statistical models constrain error ranges to as little as 20 years. Better tree-ring records have improved radiocarbon calibration, which involves matching radiocarbon dates from tree rings with the rings’ ages in calendar years. Because radiocarbon readings depend on how the atmosphere and oceans circulate the isotope around the planet, researchers must calibrate dates from the Northern and Southern hemispheres differently. Air from both hemispheres mixes over the Andes, however, so atmospheric scientists are helping archaeologists create bespoke calibration curves for major Inca sites.

Because radiocarbon dates from one site can’t be extrapolated to any other, rewriting Inca history with radiocarbon means moving city by city, monument by monument, village by village through one of the premodern world’s largest empires. “It’s one of those things we could never be finished with,” Ogburn says. “There’s always another site we could date.”

On a pleasantly sunny day in October of 2025 at 3600 meters above sea level, Peruvian archaeologist Abimael Choqque Torres was preparing to finish excavating the find of his life. He and his team were digging at Saqsaywaman, a sprawling Inca ceremonial site overlooking Cusco as part of a project supported by UW. A few weeks earlier, while excavating on top of an overgrown hill tucked away from the site’s most impressive monuments, they had caught their first glimpse of a long, pointed metal rod. Since then, they had uncovered a total of 18 metal objects.

As Choqque Torres and his team carefully removed the final metal artifacts from their resting place, he felt the weather shift. Storm clouds were gathering over the surrounding mountains. Soon, the sky cracked and hailstones pelted down. It felt like confirmation that the team had found something special—and it had.

Preliminary analyses later revealed most of the objects were made of bronze, and some of copper. They looked like tools but showed no signs of having been used before being buried. Most were rods of various lengths, some shaped into points on both ends. Others took forms archaeologists had never seen in Inca sites before, such as a small, curved spatula with serrated teeth along its edge and a flat triangle with a handle extending from one of its points.

Although organic material excavated with the offering hasn’t yet been radiocarbon dated, stratigraphy suggests the mysterious implements were buried during a sharp transition at Saqsaywaman. The site was originally dominated by large, open terraces bordered by rough walls of local rock, which were likely used to host lavish feasts intended to elevate the Incas’ status among their neighbors, says Sabino Quispe Serrano, a Peruvian archaeologist working with the UW team. But around the time of the offering, the earlier terraces were abandoned or even dismantled in favor of perfectly fitted masonry, including three zigzag walls, built in part from giant stones that had to be hauled from dozens of kilometers away. The Inca had evidently shifted from feasting with local allies to commanding the labor of a far-flung network of subordinates.

Combined with the architectural transition, the extraordinary offering suggests that at least in the Cusco heartland, the birth of the empire was as sudden as Cabello de Balboa and Rowe believed. “With this offering, they’re trying to inaugurate a new time,” Earle says. “There really is a moment where everything changes.” That pivotal period could correspond to the rise of Pachacuti, as Rowe argued. Earle points out that the name Pachacuti, which the emperor adopted upon taking the throne, means “one who turns over a new universal cycle.”

But when the UW team radiocarbon dated charcoal from its excavations at Saqsaywaman, it discovered that the site’s—and perhaps the empire’s—transformation likely took place several decades before Rowe’s start date of 1438. The researchers, including Earle, Choqque Torres, and Quispe Serrano, found that Saqsaywaman began to be remodeled around 1400, with construction kicking into high gear starting around 1418. The project’s first radiocarbon results are in press at Antiquity.

The Inca could have been on the rise even earlier, before Pachacuti was born, radiocarbon dates from beyond Cusco suggest. Marsh and fellow CONICET archaeologist Kevin Lane argue that to launch his coup as a young man in the early 1400s, Pachacuti had to be born between the 1370s and ’90s. But new radiocarbon dates from the southern part of the empire indicate Inca ceramics and architecture had already appeared at many sites in Argentina, Bolivia, and Chile by that time, more than a century before Rowe’s chronology claimed, and before Saqsaywaman’s transformation. Marsh and Lane think Pachacuti’s little-known grandfather, Yahuar Huacac, may have been the true leader of the Inca’s first push southward. Perhaps Yahuar Huacac was among the unfortunate kings largely erased from Inca history to heap more glory on his descendants.

The new early dates from the edges of the empire also change archaeologists’ vision of what Inca conquest looked like. Rowe wrote that the Inca wielded “a small but efficient army [that] could overrun vast areas and apparently powerful states quickly, and with little opposition.” But researchers can now see the expansion was far more piecemeal. Inca artifacts, infrastructure, and architecture often appeared at nearby sites decades apart and endured for significantly different lengths of time. “It’s not an army that advances town by town,” says Francisco Garrido, an archaeologist at the National Museum of Natural History in Santiago, Chile, who has excavated and dated Inca sites in northern Chile’s Copiapó Valley. “It’s more like seeds that disperse at the same time but produce something different in each place.”

The stories of the people the Inca aimed to subjugate, invisible for centuries, are also coming to light thanks to new dates—and it turns out the Inca faced far more sustained resistance than the empire would ever admit.

“Brush, brush, brush!” Elizabeth Arkush, an archaeologist at the University of Pittsburgh, clambers over a collapsed stone wall and crouches in the ruins of a small, square room. A team member hands her a paintbrush, and she gently clears earth away from a broken piece of a ceramic plate. A geometric pattern of grouped vertical lines emerges against a dark background, edged by a border of triangles.

“Certified Inca,” Pontifical Catholic University of Chile archaeologist Francisco García-Albarido declares. He found the sherd Arkush is now cleaning on his first day excavating at the site of Sicllani Incacancha this summer, more than 4200 meters above sea level on a mountaintop overlooking the Peruvian altiplano, the high plateau north of Lake Titicaca.

“I’m so jealous!” Arkush says.

At a typical excavation, one ceramic sherd wouldn’t inspire much excitement. Archaeologists can find hundreds per day in the Andes, with its high density of archaeological sites and dry, artifact-preserving climate. Arkush and co–principal investigator Sarah Kennedy, an archaeologist at Carleton College, expected the stone buildings at Sicllani Incacancha and nearby mountaintop sites to brim with plates, cups, beer jugs, and other remains of the Incas’ famous feasts, like the ones they threw at Saqsaywaman to consolidate their power. But the structures turned out to be shockingly empty. Day after day, the team dug up nothing but dirt. Without artifacts, the building’s purpose remained a mystery.

The lone ceramic, at least, emphasized who was behind its construction: the invading Inca empire. With their sharp corners, wall niches, and rectangular layouts, Sicllani Incacancha and other nearby Inca sites couldn’t be more different from the local architecture. Starting around 1300, the people of the altiplano began to live inside rambling, seemingly disorganized hilltop forts now called pukaras. Human remains from this period show a spike in violent deaths, reflecting the long tail of political turmoil ignited by an earlier drought and the collapse of the Wari and Tiwanaku states about 4 centuries before the Inca arose. Communities, including a people known as the Colla, retreated behind imposing walls to protect themselves.

Pukara walls were no match for the invading Inca, however—or at least that’s what archaeologists thought. The colonial chronicles claim the Inca quickly conquered the Colla and the other altiplano communities during Pachacuti’s reign, forcing them down from the pukaras “to live not like savages, but like men of reason,” in the words of Pedro Cieza de León, a 16th century Spanish conquistador and chronicler. Archaeologists who held to the traditional chronology assumed the lack of Inca artifacts in otherwise densely occupied pukaras confirmed the forts were hastily abandoned when the empire invaded.

But when Arkush recalibrated radiocarbon dates from both pukaras and Inca sites on the altiplano, she found the two cultures overlapped for between 30 and 60 years. Some of the largest hillforts were actively constructing defensive walls decades after the first Inca sites appear around 1400. “It’s not pre-Inca. It’s non-Inca,” Arkush says. Many pukaras represented “ongoing resistance.”

In Copiapó Valley, meanwhile, Garrido found evidence of conquered communities pushing back against imperial domination. His new radiocarbon dates for a site known as Iglesia Colorada revealed that between 1400 and ’40, the Inca aggressively remodeled the village and seemingly killed anyone who didn’t like it. Garrido studied decapitated human skulls from the site that had holes bored into them, suggesting they had been displayed as trophy heads before being discarded in a trash heap. Local people expressed their displeasure by deliberately excluding Inca ceramics from their cemeteries. “It was a form of disobedience, of not collaborating with the Inca project,” Garrido says.

The resistance may have been enough to push the Inca to rethink their approach. Garrido’s new dates from slightly later sites in the valley reveal that after 1440, the Inca concentrated their presence near a site dedicated to copper smelting, their main economic interest in the region, and left local villages to their own devices.

Perhaps a similar timeline of conflict and negotiation will emerge in the altiplano, as archaeologists continue to build the region’s chronology. For now, it seems the Inca did eventually wrest control away from the Colla. Arkush’s radiocarbon dates show people left the last pukaras around 1450, whereas altiplano Inca sites continued to be occupied. If they turn out to have been built after the Incas’ eventual victory, Sicllani Incacancha and the other mysteriously empty structures may have served to commemorate the conquest and make the empire’s unchallenged presence known across the plain below.

“Maybe building it was the point,” rather than occupying it, Kennedy proposes. “Maybe the Colla were forced to construct it.” Many of the Spanish chroniclers noted that the hill where Sicllani Incacancha is located was the site of the Collas’ last stand. Each morning on their way to the site, the archaeologists hike past a rocky pukara bristling with irregular walls that may have been the Collas’ final stronghold. Meanwhile, Sicllani Incacancha’s entryway is lined with trapezoidal niches large enough to fit a seated human body; in other parts of the empire, the Inca are known to have taken local mummies hostage and displayed them.

But it’s also possible radiocarbon dating will reveal that Sicllani Incacancha was built decades earlier, soon after the Inca arrived on the altiplano. Perhaps they did intend to use the structure for feasts as Arkush and Kennedy initially expected. Maybe it was the Colla who refused to cooperate with this imperial script, rendering the ghostly structures useless as soon as they were completed.

Only radiocarbon dates can distinguish between these possibilities, or reveal others. The day after the discovery of the Inca plate at Sicllani Incacancha, Arkush and Arizona State University archaeologist Ryan Smith gather around a niche in an interior wall. Arkush digs her trowel into the mortar between stones and dislodges dried stalks of local ichu grass, which the site’s builders added to the mixture during construction. Smith catches the plant remains in a pocket of aluminum foil, destined for a radiocarbon lab. Unlike so many Inca archaeologists before them, they have no idea what the answer will be.