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.
Rules · Doors & windows · Walls · Structure
Make every opening a trapezoid
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
The trapezoid is the Inca form par excellence: in doorways, windows and the rows of niches that line the walls of temples and halls. Inclining the jambs shortens the lintel for a given opening at the foot and wedges the jamb stones against the wall; it echoes the batter of the walls themselves. The niches held offerings and sacred objects; blind niches repeated along a wall give it rhythm, as the columns of a portico do elsewhere.
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.
Frame the doorway of a temple, palace or royal precinct with a second, larger recessed trapezoid, so that the opening steps back in two planes; keep the single jamb for ordinary buildings.
Cite this page Chris Paton, “Make every opening a trapezoid”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/inca-trapezoid. Text, drawings and models licensed under CC BY-NC 4.0.