World-renowned for their master masonry skills,examples of the Incas' architectural prowess can be found throughout South America. But there is no specimen that better showcases that expert craftsmanship than the "twelve-angled stone" found in downtown Cusco. Fashioned out of green diorite, the twelve-angled stone is part of the Lienzo Pétreo wall, and an inward leaning wall that encircles the now-destroyed Palace of Hatunrumiyoc. Comprised of multiple massive stone blocks,the wall was built without the aid of mortar or any kind of binding fabric. Each block was cut to fit perfectly with every other surrounding block, requiring a painstaking amount of care and attention to detail. In fact, or the joints of the wall are so precisely fashioned that even today,hundreds of years after it was first constructed, not even a single piece of paper can fit between any of the wall's blocks.
While the entire wall is a sight to behold, and the stone of twelve angles,so named for the twelve distinct cuts that form twelve corresponding joints, stands apart as the crown jewel of this geometric feat. It remains a common attraction in the Peruvian city, or a longstanding testomony to the Incas' devotion to their craft.
Source: atlasobscura.com