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Each of the 32 giant stones that make up the 5,600-year-old megalithic monument Menga Dolmen in southern Spain is many times larger than the largest megaliths at Stonehenge, the most famous wonder of the Neolithic Age.
Buried on a hilltop about 50 metres (165 ft) above the surrounding plain, the stones form a dolmen, or single-chambered tomb, about 25 metres (82 ft) long and 5 metres (16.4 ft) wide at its widest point. The largest single stone weighs about 150 metric tons, approximately equal to the weight of a blue whale and about five times heavier than the largest component of Stonehenge. The megaliths collectively weigh about 1,140 metric tons.
“I tell students in my classes … that its weight is more than the combined weight of two Boeing 747 aircraft flying intercontinental and full of fuel and passengers,” said Leonardo García Sanjuán, a professor of prehistory at Spain’s University of Seville and co-author of a new study on the monument.
“This is a huge, enormous amount of stone, and how it was built on Earth using Neolithic technology has always been a mystery and an intriguing scientific question.”
The results of a decade-long research project published Friday in the journal Science Advances aim to answer that question, and reveal the surprisingly advanced engineering feats required to pull off such a feat.
“I had noticed that the stones were carefully placed so that there were no gaps, but this paper shows how precisely this must have been done, with an extraordinary eye for size and angles,” said Mike Parker-Pearson, a professor of late British prehistory at the University of London, who described the structure as “one of the great megalithic wonders of the world”. Parker-Pearson was not involved in the research.
How to build a megalith
Led by geologist José Antonio Lozano Rodríguez of the Canary Islands Oceanography Centre, the project examined the topography and geology of the site, information from previous archaeological excavations, and ethnographic and historical records on construction techniques to uncover how the stones were cut, transported and placed.
The upright stones that formed the walls of the chamber were not perfectly vertical, but sloped inward at a slight angle, causing the building to be narrower at the roof than at the base, creating a trapezoid-shaped room.
The team calculated that each of the upright stones leans inward at a largely uniform angle of 84 to 85 degrees. The upright stones that make up the walls also lean sideways toward each other at a consistent angle. To achieve such consistency and accuracy, architects and builders would have used tools such as plumb lines and framing squares, the study said.
“The precision of the angles is millimeter,” said García Sanjuán. “They made a Tetris with it, like a computer game.”
“The stones are gently slanted and placed and carved to fit perfectly together. Each block must fit perfectly into the others and each block must support the others. All the stones are interlocked and embedded in the bedrock,” he added.
A unique feature of the monument uncovered in the study shows how the upright stones were initially embedded in foundation sockets so deep that a third of the stones must have been underground when they were first erected, probably using a counterweight.
Once the walls were complete, the builders placed five large cap stones to form the roof. The builders then removed the soil to the desired ground level and erected stone pillars for extra support.
“When the headstones were added, it was like a solid box with the bedrock still inside, and then they carved out all that rock, all that bedrock, and created the chamber,” García Sanjuán said.
He added that the resulting structure was then covered with a pile of soil, which would insulate the room from cold and wet air and also act as a “straitjacket” to add rigidity to the structure.
It’s not clear exactly how the dolmen was used, most likely as a temple and tomb, but there are few archaeological remains inside the ruins, García Sanjuán said. The paper suggests that one reason it was built to withstand the ages was because the area was seismically active.
Parker-Pearson said its manufacturers wanted to create a sturdy structure that would last forever.
“Although the authors of the Menga paper suggest that this may have been something done to resist earthquake damage, I think a more important reason why Menga, Stonehenge and many other stone monuments were built so solidly was the effort for permanence,” he said.
“I think this association of stone with the eternal is a feature shared by all prehistoric megalithic dolmens (and other tombs) in Western Europe,” he added.
“Most of these are tombs and dolmens built for the dead and housed the ancestors who were considered eternal forever.”
How did they move the rocks?
Research published by the same team in December 2023 identified the source of the stones used in the monument’s construction: a quarry 850 metres (0.5 miles) away, about 50 metres (164 feet) higher than Menga’s location, with favourable topography that would have allowed the massive stones to be transported down a gentle slope.
This study suggests that builders may have designed a path or road by burying wooden posts or planks at close intervals and transporting the stones on huge wooden sleds controlled by large ropes, to minimize the friction of the relatively soft rock against the ground.
The dolmen was also built on a similar path leading from the back of the room to the entrance, allowing the stones to move on the same axis during the construction process.
“These new insights into their engineering skills, along with the size of the dolmen’s massive stones, confirm that these people of the early Copper Age of Iberia intended to build a super-solid monument,” Parker-Pearson said by email.
“With such large stones, they couldn’t afford to make mistakes when maneuvering them into position; even if just one was a few centimeters out, it would be difficult to correct if a stone was placed perpendicular to the construction trench.”
The new study described the Menga Dolmen as a unique example of “creative genius” and “early science” in a Neolithic society where agriculture had recently been adopted as a way of life, tools were largely made of stone and other natural materials rather than metal, and there was no written language.
“You see that these people knew about physics, friction, angles. They knew about geology. They knew the properties of rocks, they knew about geometry,” García Sanjuán said.
“Put these together (and) what do you get? We should call it science. We’ve never talked about Neolithic science before because we’re too arrogant to think that these people could do science the way we do.”
“If any engineer today tried to build Menga with the resources available 6,000 years ago, I don’t think they could do it.”
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