The reason the Incas built Machu Picchu on two fault lines

The fault of the Earth’s crust provided a suitable source of granite to help the Incas save energy to build the ancient citadel of Machu Pichu.

Rualdo Menegat, a geologist at the Federal University of Rio Grande do Sul, presented the new discovery about the ancient citadel of Machu Picchu at the annual meeting of the American Geological Society earlier this week. Using satellite imagery and field data, Menegat examines the network of faults beneath Machu Picchu, from a small crack running across the boulders to a 172km-long fault in the river valley.

The reason the Incas built Machu Picchu on two fault lines
The ancient citadel of Machu Picchu. (Photo: Smithsonian).

Some fissures run in a northwest-southeast direction while others run in a northwest-southwest direction. In the middle, where two large cracks intersect in an X shape is Machu Picchu. According to Menegat, it is more likely that the Incas chose the rift network not for religious or symbolic reasons. Instead, the fault broke the granite rocks into small pieces, saving energy in the process of building stone settlements. The walls of the citadel also rotate in the direction of the fault.

“The location of Machu Picchu was not chosen by accident. The strong faulting there caused the rock to crack along the plane, thereby reducing the work of the Incas,” Menegat said.

In addition to allowing the Incas to easily find and put together blocks of stone without the use of mortar, faults provided many other benefits. The fault line runs through the area leading melted snow and rainwater to the settlement. The network of cracks beneath Machu Picchu also helps to absorb water. This is one of the reasons the building has been able to last so long.

“It seems to me that no civilization could have formed in the Andes without knowing the rocks and mountains of the region. Machu Picchu is not an isolated case of the Incas’ strategy of survival in the Andes.” Menegat said.

Other Inca citadels include: Ollantaytambo, Pisac and Cusco, all built at the intersection of fault lines. This does not indicate that the Incas had a deep understanding of plate tectonics. Most likely they were just looking for areas filled with triangular and diamond-shaped broken rock that could be put together to build walls.

Archaeologists believe that Machu Picchu was built around 1450 by order of Emperor Pachacuti Inca Yupanqui. The citadel is said to have been the residence of the emperor and the Inca aristocracy. When the Spaniards invaded South America, war and disease caused the Inca Empire to collapse. Machu Picchu and many other places were abandoned. In 1911, professor Hiram Bingham III of Yale University discovered the weed-covered ruins of the settlement thanks to the guidance of local people. Today, Machu Picchu is a World Heritage Site and is threatened by overcrowding.