The Seismic Dance of Stones
Inca engineers built Machu Picchu in a region of high seismic activity. Rather than rigidly opposing the earth's movements, their structures are designed to move with them. This is possible through a masonry technique called ashlar, where stones are cut with such precision that they fit together perfectly without mortar. During an earthquake, the stones can move and shift, dissipating the seismic energy, before settling back into their original positions. This phenomenon is often described as the "dancing stones."
The design features trapezoidal shapes for doors, windows, and the walls themselves. Walls lean inward, typically between 3 and 5 degrees, which lowers the building's center of gravity and provides exceptional stability during a tremor. A major earthquake with a magnitude of at least 6.5 struck the site around 1450 during its construction. This event likely prompted Inca builders to perfect the seismic-resistant techniques seen today, moving from smaller stones to the massive, interlocking polygonal blocks that define the site. The stones are often multi-cornered and fit together like puzzle pieces, increasing the structure's integrity.