At first, the reeds festooned with human vertebrae and skulls seemed too macabre to be anything more than a sick joke. When archaeologist Jacob Bongers and his team came across the strange sight in Peru’s Chincha Valley, they chalked it up to looters who had come before, disturbed ancient tombs in the area, and left the reeds as a calling card. The locals knew all about the skeleton sticks — but when Bongers asked about them, all they told him, he says, was that “they’re antiguo. They’re definitely old.” But beyond that, their origin and purpose remained a mystery to the archaeologists — one they became determined to solve.

The anthropological archaeologist, who works at the University of East Anglia, says part of the mystery came from the fact that the Chincha valley was well-trodden ground for archeologists. Surely, he supposed, someone must have noticed the reeds covered in disarticulated human vertebrae?

“We aren’t the first people to do fieldwork in this valley, so why weren’t they documented before by other scholars?” Bongers tells Inverse. Since he came upon a post for the first time in 2012, Bongers has found 200 of these skeletal posts at dozens of mortuary sites in Peru.

One might think that posts threaded with pieces of human backbone would inspire curiosity, but Bongers believes he and his team are the first to systematically analyze these bones. In a new study published in the journal Antiquity, Bongers and his team detail results from their analysis of a subsample of bones collected at 79 posts with radiocarbon dating methods. Armed with these data, he thinks he may have solved where the bones came from.

The discovery — By calculating the approximate age of the bones and reed posts, Bongers hypothesizes the posts may have been created by indigenous people in an effort to reconstruct the bodies of ancient Peruvians, who once laid in tombs looted by Spanish colonizers. The bones themselves date back to between 1520 and 1550 C.E., while the reeds come from a later era, between 1550 and 1590. This age gap is critical to supporting Bongers’ theory.

The bones offer insight into the chaos wrought by colonists in South America; but also a slew of gruesome events within the contemporary Chincha Kingdom itself.

The Chincha Kingdom had presided over the land where the bones now lie until the 1400s, when it melded with the Inca Empire. At that time, the indigenous people suffered famines and outbreaks of disease, causing many to perish. When European colonizers arrived in the 1500s, they looted chullpas, or ritual tombs, for gold and silver. They often disturbed the human remains within the tombs, too.

Why it matters — Bongers argues the decorated reeds may have been erected by the indigenous peoples are a way to literally rebuild their dead in response to the colonizers’ atrocities.

“What this finding speaks to is indigenous people adapting to harsh circumstances and finding a way to maintain connections with their dead,” he says.

“These body parts continue to live these social lives,” Bongers says. Essentially, the bone-stacked posts tell a story of how a civilization responded to invasion and death.

Beth Scaffidi, an anthropologist at the University of California at Merced who was not involved in the study, agrees.

“Ancient bodies in the imagination are not these things that just sit there,” she tells Inverse. “They are animated, every body part, even the vertebrae. So there is a world in which we can see that explanation where they’re reforming these bodies as a way to resist or conquer colonial looting practices.”

Digging into the details — Scaffildi says Bongers’ hypothesis fits in with what we know about how the dead were treated in this region at the time. Andean peoples have long venerated their dead with specific rituals.

The discrepancy between the reeds’ and bones’ ages supports Bongers’ theory.

“Even before the dates came back, it was like, ‘This is sort of a wacky theory. What if this is what actually transpired?’” Bongers tells Inverse. The fact that the bones are older than the reeds, and the reeds’ date coincides with colonization supports a narrative that the colonizers disturbed tombs of the already-dead, and the natives rebuilt their backbones.

“This was a sort of indigenous, ritualized response to European colonialism.”

There are a few clues to suggest that these erected posts are reconstructed. For one, the vertebrae are disarticulated, or separated at the joint. Each vertebra is disconnected, and someone arranged them on a post — not necessarily in their original order. This suggests that whoever built these posts was using bones that were already disconnected from one another — perhaps destroyed due to colonizers.

Still, there are other explanations as to who erected these posts and what their purpose was that are worth considering, Bongers says.

“My personal favorite is… that they may have been rattles that were used in mortuary ceremonies,” Bongers says. Or, they could have been trophies to boast conquest of their enemies.

Scaffidi says it’s possible that these artifacts played all these roles at once, and these different roles in cultural life are not mutually exclusive. A trophy of an enemy warrior could have been rebuilt as a statement of defiance in the face of the colonizers, she theorizes.

What’s next — While these bones have continued living social lives for centuries, their time as windows into the past has just begun. Bongers says a future study might conduct DNA analysis on these bones, which could help answer the question of whether the chullpas were family tombs, or, on the other hand, were more like mass graves.

According to Scaffidi, preserved vertebrae can be “kind of crumbly,” but they can also offer telling insights into how people lived, too. The bones can reveal new details about a person’s diet in the last year of their life, for example, and that offers clues as to their social standing and role in the culture. While all this information separately may seem like mere trivia, together they paint a rich, detailed picture of a civilization at a pivotal time in history.