How it works
Start with an equilateral triangle and join the midpoints of its sides. This creates four equal triangles. Remove the central one, leaving three corner triangles. Repeat inside every surviving triangle. Here, the remaining triangles are drawn as outlines.
Where it began
Polish mathematician Wacław Sierpiński described the construction in 1915. Finite patterns with the same nested arrangement appeared much earlier, including in medieval Italian decorative art. The mathematical study and the visual motif have different histories.