The Menga dolmen (Antequera, Malaga) is the oldest and largest of those found on the Iberian Peninsula. It was built between 3,800 and 3,600 BC and is crowned by five large slabs. Until now, experts wondered how it was possible that, in the Neolithic period, more than a thousand years before the first pyramids of Egypt were built, these enormous stones could be moved and placed with millimetric precision, orienting them towards dawn for astronomical purposes.
Ten years of research, captured in a study published this Friday by the magazine Science Advances, The Spanish researchers who wrote the article say that the extraordinary dimensions of some of the dolmen’s structural parts required sophisticated design and planning, a large mobilisation of manpower and perfectly executed logistics.
The Menga dolmen is located on the top of a hill that rises about 50 metres above the plain of the valley of the river Guadalhorce. It is a megalithic gallery monument, 24.9 metres long, with a maximum width of 5.7 and a height that varies between 2.40 and 3.50 metres. Access to the interior space is through a small roofless atrium. It preserves three aligned pillars, although it possibly had a fourth. The 32 stones that make it up weigh about 1,140 tonnes. Of these, the largest and the one that covers the back of the chamber, weighing 150 tonnes, is the largest moved during the megalithic phenomenon in the Iberian Peninsula and the second largest in Europe, only surpassed by the Great Menhir Brisé (south of Brittany, France).
José Antonio Lozano Rodríguez, the main author of the study, a researcher at the CSIC and member of the Department of Prehistory at the University of Alcalá de Henares, explains that to build the dolmen, “soft or moderately soft stones were used, which indicates that they had spectacular engineering knowledge. The problem was that they had to be transported without breaking, taking into account that it was a porous material. Therefore, everything was planned from the quarry, thanks to the sophisticated knowledge of engineering, geology, geometry and astronomy that its builders had.” This expert points out that the first thing that was done was to prepare a smooth pavement so that the stones would not vibrate, and then this was leveled with crossbeams so that the sleds on which they were mounted could slide easily.
Since there was no heavy machinery in the Neolithic period to lift such a huge stone, it was decided to bury the megalithic building, made up of orthostats – blocks of stone placed vertically. In this way, the convex slabs of the roof could be slid over the orthostats and pillars, without having to climb ramps.
The enormous pressure exerted by the slabs and the mound that covers it caused the engineers to design the orthostats with an inclination of between 83 and 86 degrees, so that they would rest on each other and the building would be able to join together to form a unit. “The inclination unified all the orthostats and created a homogeneous distribution of stress,” explains Lozano. To prevent the slabs from breaking in the centre, pillars were placed and the upper face of the covers, especially the heaviest slab, was given a convex shape. They thus acted as relieving arches, just as occurs in the roof of medieval and modern cathedrals, thus managing to transfer the stresses towards the orthostats. “This is the first proven use of the principle of the relieving arch, almost 6,000 years ago. It is one of the first complex stone buildings in the history of humanity,” explains the researcher.
The study adds that the engineering design and its orientation “towards the mountain of Peña de los Enamorados and with a solar significance” demonstrates that in the Neolithic there was already scientific knowledge of extraordinary precision and inventive brilliance. The Menga dolmen shows an astronomical alignment: its solar orientation means that, during the summer solstice, the left side of the inner chamber remains in shadow; meanwhile, a large part of the right side remains illuminated.
Megaliths are structures made of large stones and are found in a variety of regions around the world, most notably in late prehistoric Europe (Neolithic, Copper Age, Bronze Age and Iron Age), where megalithic monumentality was widespread. Humanity’s earliest monumental stone constructions also contain profound social and ideological messages that are enduring and visible. The longevity of large stones (as opposed to wood) and their visual impact on the surrounding landscapes suggest that long-term persistence was an important driver of their construction.
The megalithic site of Antequera includes two natural formations (the Peña de los Enamorados and the karstic massif of El Torcal), as well as four large monuments: the aforementioned Menga dolmen, the Viera dolmen, the tholos circular of El Romeral and the recently discovered megalithic hypogeum of Piedras Blancas, located at the foot of the Peña de los Enamorados.
Menga is unique for its time for several reasons, according to the study signed by experts from the CSIC and the universities of Alcalá, Salamanca, Seville and Granada. The use of pillars to support the gigantic cornerstones and the embedding of a large part of the building in the bedrock to achieve stability, as well as the perfect fit of the orthostats with each other, make it a monument with “characteristics that are not seen in any other megalithic construction”.
A deep knowledge of the properties and location of the available rocks, basic physics notions (friction, activation energy, optimal slope of the ramp, estimation of the centre of mass or load capacity of the available rocks) make it unique and demonstrate mastery of, among other disciplines, geometry, engineering and astronomy. For the researchers, all of this is confirmed by “the precise alignment of the central axis of symmetry of Menga at 45 degrees, thus coinciding with the natural orientation plane of the northern cliff of Peña de los Enamorados to which the dolmen is oriented.”
The authors believe that, due to the accumulation of advanced knowledge in various fields of geology, physics, mathematics and astronomy, this dolmen not only represents a feat of early engineering, but also a substantial step in the advancement of human science. “Menga demonstrates the successful attempt to make a colossal monument that would last for thousands of years,” the study concludes.
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