Inca masonry
Walls fitted without mortar (polygonal or coursed), with the inward-leaning trapezoidal doorways and niches of Inca architecture.
The rules it illustrates
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.
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.
Lean the walls inward. Batter every wall a few degrees, thicker at the foot than at the top, and round its outer corners.
Coursed ashlar for the holiest places. 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.
Double the jamb to mark rank. 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.
Where it appears in the book
In the styles Andean.
In the chapters The Americas.