The ancient Incas were skilled stonemasons, and the technology they used to build their structures is still a mystery. Samples of their architectural skill can be seen all over South America, and one of the most striking examples of the Inca’s incredible craftsmanship is the “twelve-cornered stone” found in the center of Cusco.
The twelve-angled stone, carved from green diorite (Mohs hardness, 8.5), is part of the Lienzo Petreo, a wall that slopes inward and surrounds the palace of Hatunrumiyoc, destroyed by the colonizers.
The wall was built without the use of cement or other bonding material, each stone being carved in perfect harmony with the shape of the surrounding blocks.
The joints in the wall are made with incredible precision, making it impossible to slip even a piece of paper between the blocks. It is the twelve-cornered stone, which gets its name from the twelve distinct facets that form the corresponding joints, that is the real gem of this geometric marvel.
The twelve corners of the stone are admired for their meticulous workmanship and perfect correspondence to form. Today, the stone with twelve corners is part of the wall of the Archbishop’s palace.