Give doors, windows and niches sides that lean inward, so that each opening is narrower at the top than at the bottom, and span it with a single stone lintel.
top width ≈ ⅘ of bottom width
Rules · Walls · Materials · Structure
Fit every stone to its neighbours
Shape each block of the finest walls to the irregular outline of the stones already laid, grinding the joints until they close without mortar; let the stones be as large and as many-sided as they come.
In Inca polygonal masonry (the walls of Sacsayhuamán above Cuzco, the street wall of Hatunrumiyoc with its famous twelve-angled stone) no two blocks are alike and no joint runs straight for long. Each stone was repeatedly lowered, checked against the bed and neighbours, lifted, and pounded or ground with harder hammerstones until the faces met. The faces were left slightly pillowed, so that every joint is a sharp shadowed line.
Garcilaso, who played among the ruins as a boy, marvels at the size of the stones at Sacsayhuamán and at how closely they were fitted without mortar, iron tools, draught animals or wheels. The interlocking shapes also resist the earthquakes of the Andes: the stones can shift and settle back into place.
Related rules
Batter every wall a few degrees, thicker at the foot than at the top, and round its outer corners.
batter ≈ 3–5°
For the most sacred buildings lay rectangular blocks in level courses that diminish in height towards the top of the wall, with pillowed faces and joints closed without mortar.
Cite this page Chris Paton, “Fit every stone to its neighbours”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/inca-polygonal-fit. Text, drawings and models licensed under CC BY-NC 4.0.