The Pythagorean decad — ten dots in a triangle encoding the cosmos.
The Tetraktys arranges the first four numbers as a triangle of ten points — one, two, three, four — and in that small figure the Pythagoreans found the whole cosmos: the octave, the fifth, the fourth, the ratios that make music and order. It is the claim that number is not description but substance, that reality is built from proportion.
The Tetraktys unlocks a way of seeing structure beneath appearance — of trusting that harmony, intervals, and relationships can be counted. It is the ancestor of every belief that the world is, at bottom, mathematical.