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This theory suggests few workers were needed to cap Easter Island statues

People might have pulled cylinders up a ramp with ropes, then tipped the ‘hats’ onto statues

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7:00am, June 8, 2018
Easter Island statues

ISLAND WEAR  A new analysis concludes that colossal stones placed on top of some Rapa Nui, or Easter Island, statues were rolled up earthen ramps by small groups of people using only long ropes.

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The story of how some of the massive stone statues on Rapa Nui, also known as Easter Island, ended up wearing stone hats involves ramps, ropes and remarkably few workers, a contested new analysis suggests.

No more than 15 people were needed to manipulate ropes that rolled stone cylinders, or pukao, up ramps to the top of forward-leaning statues, say archaeologist Sean Hixon of Penn State and his colleagues. The hatlike cylinders were then tipped over to rest atop statues, the researchers propose online May 31 in the Journal of Archaeological Science.

After clearing the ramp away, workers then carved statues’ bases flat so that the figures assumed their iconic, upright positions.

Several possible ways in which Rapa Nui inhabitants put pukao on statues have previously been proposed, including sliding pukao up wooden ramps.

“Our group is the first to consider which pukao transport and placement scenario is most consistent with the archaeological record of these multi-ton objects,” Hixon says. The researchers accounted for possible ways in which stone cylinders with the physical features of pukao could have been leveraged onto statues’ heads.

Covering just 164 square kilometers, Rapa Nui sits in the Pacific Ocean about 3,700 kilometers west of Chile. Polynesian travelers first reached the island by the 1200s (SN Online: 1/5/15).

Those people made nearly 1,000 human statues from volcanic rock. Hundreds of them, measuring up to 10 meters tall and weighing up to 74 metric tons, were moved to stone platforms, many on the coast. A team led by study coauthor Carl Lipo of Binghamton University in New York concluded in 2013 that islanders used ropes to rock upright statues enough so that the huge stones waddled down prepared dirt roads to display sites. Some statues fell along the way and were left on the side of the road. Those left-behind rocks reveal bases carved on a slight diagonal rather than flat.

Rock 'n' roll

A new proposal for how Rapa Nui islanders placed colossal hatlike cylinders atop massive statues suggests few people were needed. In this diagram, a team of workers uses a rope technique called parbuckling to roll a cylinder up a makeshift ramp to a forward-leaning statue. Carvers then evened out the base of the statue so it stood upright.

Rapa Nui islanders diagram

The pukao were carved from a distinctive, red-hued rock. Weighing up to nearly 12 metric tons, the cylinders were probably laid on their sides and rolled down dirt roads to statue sites, where they were carved into their final shapes, the researchers say. Rock chips are still scattered around the statue sites from that activity.

Ramps made of soil and stones provided access to the tops of statues, Hixon’s group proposes. A technique called parbuckling would have enabled a small group of people to roll cylinders up ramps. In that scenario, islanders would have wrapped a long, doubled-over rope made from a local shrub around a cylinder placed on its side. One of the rope’s ends would be anchored at or near the ramp’s top and held in place by several individuals. Another group would have pulled on the rope’s free end to roll the cylinder uphill.  

At the top of the ramp, islanders would have tipped the pukao into place on a statue’s head, although it’s unclear precisely how the tipping was done. Shallow indentations on the bottoms of cylinders, identified on 3-D models of 10 pukao left at a quarry site, enabled a snug fit atop the statues, the researchers say.

Archaeologist Jo Anne Van Tilburg of UCLA regards the new scenario as dubious. Base angles on Rapa Nui statues varied considerably, making them difficult and dangerous to maneuver upright, Van Tilburg says. And parbuckling pukao up long ramps would not have reduced the total effort required to move the massive cylinders to where they needed to be, she contends.

A more plausible plan, in Van Tilburg’s view, involved transporting statues and pukao together. Van Tilburg directed a 1998 experiment in which a tree-trunk frame was used to transport a replica stone statue and pukao to an experimental platform. Ropes were used to pull the frame-encased replicas, lying prone, across the rungs of a wooden, ladderlike ramp up to the platform. Six to eight families could have completed this process, she estimates.

However Rapa Nui’s statues and pukao were moved and set up, they along with other impressive stone monuments, such as England’s Stonehenge (SN Online: 9/6/12), were built by small communities rather than states or kingdoms, Lipo says.

Citations

S.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.

C.P. Lipo, T.L. Hunt and S. Rapu Haoa. The ‘walking’ megalithic statues (moai) of Easter Island. Journal of Archaeological Science. Vol. 40, June 2013, p. 2859. doi: 10.1016/j.jas.2012.09.029.

Further Reading

B. Bower. Stones challenge dating of Easter Island collapse. Science News Online, January 5, 2015.

B. Bower. Herders, not farmers, built Stonehenge. Science News Online, September 6, 2012.

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