Take a triangle and cut a smaller triangle out of its middle; three smaller triangles remain. Do the same to each of those, then again, without end. Every corner of the result holds a half-sized copy of the whole, meaning that the small details echo the larger design.

Wacław Sierpiński described this shape in 1915, and it became one of the first fractals mathematicians learned to recognize.

But its beauty was recognized long before its mathematics had a name. Centuries before Sierpiński described it mathematically, medieval craftspeople laid a version of this pattern into the mosaic floor of Italy’s Anagni Cathedral.

This pattern has a practical side, too: engineers use its nested triangles to make antennas that pick up signals at different frequencies.