The Incan civilisation built their mountain-topping citadel of Machu Picchu on the intersections of tectonic fault lines deliberately, a researcher has argued.
The setting of the 569-year-old city would have provided an abundance of easy-to-work building stone that was predisposed to fracturing in the direction of the faults.
Additionally, the fault network likely provided a source of water, channelling both fresh- and meltwater to the site and draining away rain during storms.
The finding helps to explain why the Incan city was built in such an inaccessible location — atop a ridge above a river canyon high in the Peruvian Andes.
A number of other Incan settlements are also built atop of the intersection of tectonic faults on the Earth’s surface, the researcher added.
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The Incan civilisation built their mountain-topping citadel of Machu Picchu on the intersections of tectonic fault lines deliberately, a researcher has argued
Geologist Rualdo Menegat of the Federal University of Rio Grande do Sul in Brazil combined satellite images of Machu Picchu with field measurements to map out the fractures and faults that underlie the famous UNESCO World Heritage Site.
He found that these tectonic features come in various sizes at the site — ranging from tiny fractures visible in individual blocks of rock to massive-scale faults.
The latter reach up to 109 miles (175 kilometres) in length and have determined the layout of some of the river valleys that cross the region around the Incan citadel.
Some of the faults were created by the tectonic activity which lifted up the Central Andes Mountains across the last eight million years.
Dr Menegat found that these features appear in several sets — with some running in a northeast–southwest direction and others northwest–southeast.
Together, these lines intersect beneath Machu Picchu, creating an ‘X’ shape.
Dr Menegat also found that the citadel’s urban sectors, individuals buildings, stair and surrounding agricultural fields were also all aligned with these major faults.
‘The layout clearly reflects the fracture matrix underlying the site,’ said Dr Menegat, who added that other Incan cities are also built on the intersection of faults.
These include Cusco, Ollantaytambo and Pisac.
‘Each is precisely the expression of the main directions of the site’s geological faults,’ he added.
Furthermore, Dr Menegat believes that the underlying network of faults and fractures were integral to the construction of Machu Picchu itself.
‘The intense fracturing there predisposed the rocks to breaking along these same planes of weakness, which greatly reduced the energy needed to carve them.’
Dr Menegat found that these features appear in several sets — with some running in a northeast–southwest direction and others northwest–southeast. Together, these lines intersect beneath Machu Picchu, creating an ‘X’ shape
‘The layout clearly reflects the fracture matrix underlying the site,’ said Dr Menegat, who added that other Incan cities are also built on the intersection of faults
Machu Picchu’s stonework is legendary — the blocks were put together without mortar so perfectly that it is impossible to even slide a credit card between them
The Incas would have taken advantage of this abundance of easily workable building materials, Menegat said.
Machu Picchu’s stonework is legendary — the blocks were put together without mortar so perfectly that it is impossible to even slide a credit card between them.
‘Machu Picchu’s location is not a coincidence,’ said Dr Menegat.
‘It would be impossible to build such a site in the high mountains if the substrate was not fractured.’
The web of faults beneath Machu Picchu likely furnished the Incan people with other benefits as well, Dr Menegat said — with a water supply being the most beneficial.
‘The area’s tectonic faults channelled meltwater and rainwater straight to the site,’ he added.
Furthermore, Dr Menegat believes that the underlying network of faults and fractures were integral to the construction of Machu Picchu itself
The setting of the 569-year-old city would have provided an abundance of easy-to-work building stone that was predisposed to fracturing in the direction of the faults
Another advantage in building at the Machu Picchu site would have come from how the citadel’s high perch effectively isolated it from avalanches and landslides.
These, Dr Menegat explained, are common hazards in this alpine setting.
Alongside this, the fractures beneath the citadel would have helped to drain the settlement during the intense rainstorms which frequently hit the region.
‘About two-thirds of the effort to build the sanctuary involved constructing subsurface drainage,’ said Dr Menegat.
‘The preexisting fractures aided this process and help account for its remarkable preservation.’
‘Machu Picchu clearly shows us that the Incan civilisation was an empire of fractured rocks.’
The full findings of the study were presented on September 23 during the 2019 annual meeting of the Geological Society of America held in Phoenix, Arizona.
The finding helps to explain why the Incan city was built in such an inaccessible location — atop a ridge above a river canyon high in the Peruvian Andes
