The ancient people of Easter Island, Chile, were able to move so-called pukao — massive stone hats of the island’s famed monumental statues (moai) — and place them on top of the statues with minimal labor and resources, using a parbuckling technique, according to new research published in the Journal of Archaeological Science.

“Of the many questions that surround Easter Island’s past, two tend to stand out: how did people of the past move such massive moai and how did they place such massive pukao on top of their heads?” said Binghamton University’s Professor Carl Lipo, co-author of the study.

Easter Island’s moai, carved from volcanic tuff, came from one quarry on the island, while the pukao — cylinders made of red scoria, some of which weigh up to 12 tons — came from a different quarry 7.5 miles (11.2 km) away on the other side of the island.

They were moved all around the island, across long distances, with few people and resources.

Previous research by Professor Lipo and colleagues determined that the statues, which can be up to 33 feet (10 m) tall and weigh 81 tons, were moved into place along well-prepared roads using a walking/rocking motion, similar to the way a refrigerator is moved.

“The moai were moved in a fashion using simple physics-based processes in a way that was elegant and remarkably effective. Not all statues made it to their final locations, and the fallen and/or broken ones showed that, to move them, the statues were carved so they leaned forward and were later leveled off for final placement,” Professor Lipo said.

The pukao, with diameters up to 6.5 feet (1.8 m), might have been rolled across the island, but once they arrived at their intended statues, they still needed to be lifted onto the statues’ heads.

The ancient Easter islanders probably carved the pukao cylindrically and rolled them to the statues before further carving the hats to attain the final shapes, which vary from cylindrical to conical and which usually have a smaller cylindrical projection on the top. Chips of red scoria are found in the platform of some of the statue hat combinations.

“We were interested in figuring out the method of hat transport and placement of the hats that best agrees with the archaeological record,” said lead author Sean W. Hixon, graduate student at Pennsylvania State University.

The researchers took multiple photographs of 50 pukao found across the island and 13 red scoria cylinders from Puna Pau, the island’s pukao quarry, to see what attributes of the objects were the same throughout.

Using photogrammetry and 3D imaging, they created images of the objects with all their details.

“We assumed they were all transported and placed in the same way. So we looked for features that were the same on all the hats and all the statues,” Hixon said.

The only features the team found the same were indentations at the bases of the hats, and these indentations fit the tops of the statues’ heads.

If the hats had been slid in place on top of the statues, then the soft stone ridges on the margin of the indentations would have been destroyed. So the islanders must have used some other method.

“The best explanation for the transport of the pukao from the quarry is by rolling the raw material to the location of the moai,” Professor Lipo said.

“Once at the moai, the pukao were rolled up large ramps to the top of a standing statue using a parbuckling technique.”

Parbuckling is a simple and efficient technique for rolling objects and is often used to right ships that have capsized.

“In parbuckling, a line would have been wrapped around the pukao cylinder, and then people would have pulled the rope from the top of the platform,” Professor Lipo said.

“This approach minimizes the effort needed to roll the statue up the ramp. Like the way in which the statues were transported, parbuckling was a simple and elegant solution that required minimum resources and effort.”

“This use of resources shows how efficiently the people of Easter Island used their resources, which contrasts with what was previously thought,” he added.

“Easter Island is often treated as a place where prehistoric people acted irrationally, and that this behavior led to a catastrophic ecological collapse. The archaeological evidence, however, shows us that this picture is deeply flawed and badly misrepresents what people did on the island, and how they were able to succeed on a tiny and remote place for over 500 years.”

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Sean W. Hixon et al. The colossal hats (pukao) of monumental statues on Rapa Nui (Easter Island, Chile): Analyses of pukao variability, transport, and emplacement. Journal of Archaeological Science, published online May 31, 2018; doi: 10.1016/j.jas.2018.04.011