Dry-stone walls control

People of Inca civilization were masters of the polished dry-stone walls, called ashlar, where blocks of stone were cut to fit together tightly without any mortar. The Incas were among the best stone masons the world has ever seen, and many junctions in their masonry were so perfect that even blades of grass could not fit between the stones.

Peru is a highly seismic land, and for centuries the mortar-free construction proved to be apparently more earthquake-resistant than using mortar. The stones of the dry-stone walls built by the Incas could move slightly and resettle without the walls collapsing which should be recognized as an ingenious passive vibration control technique employing both the principle of energy dissipation and that of suppressing resonant amplifications.