http://www.sciencemag.org/news/2019/10/machu-picchu-was-hit-strong-earthquakes-during-construction > The Incan citadel of Machu Picchu in Peru is known for its marvelous stonework. But several structures at the site suffered through at least two earthquakes as they were being built, a new study suggests. Those temblors not only damaged walls, but also triggered a sudden change in construction techniques. > The study—an archaeological survey of three of Machu Picchu’s most significant temples—reveals more than 140 examples of damage. These include large blocks of stone that have shifted or whose corners have been chipped. Some of this damage can be attributed to slumping rocks or soil beneath the temples. But the movement of many damaged blocks, including substantial gaps between some formerly interlocking blocks of stone, was likely driven by seismic shaking from at least two major quakes, the team concludes. That’s because the type of damage seen on the corners of blocks embedded in the stone walls only occurs as they rhythmically clatter against each other during an earthquake, researchers report this month in the Journal of Seismology.