tetractys

thumb|200px| The tetractys The tetractys (), or tetrad, or the tetractys of the decad is a triangular figure consisting of ten points arranged in four rows: one, two, three, and four points in each row, which is the geometrical representation of the fourth triangular number. As a mystical symbol, it was very important to the secret worship of Pythagoreanism. There were four seasons, and the number was also associated with planetary motions and music.

==Pythagorean symbol== The first four numbers symbolize the musica universalis and the Cosmos as: Monad – Unity Dyad – Power – Limit/Unlimited (peras/apeiron) Triad – Harmony Tetrad – Kosmos The four rows add up to ten, which was unity of a higher order (The Dekad). The Tetractys symbolizes the four classical elements—air, fire, water, and earth. The Tetractys represented the organization of space: the first row represented zero dimensions (a point) the second row represented one dimension (a line of two points) the third row represented two dimensions (a plane defined by a triangle of three points) the fourth row represented three dimensions (a tetrahedron defined by four points)