The Tetractys — Sacred Ten

The Tetractys (tetraktys tes dekados) is the triangular arrangement of ten points in four rows (1+2+3+4=10) that the Pythagoreans regarded as the most sacred symbol of their school. According to Iamblichus (Life of Pythagoras), the community swore their binding oath 'by him who transmitted the Tetractys to our soul.' It encodes the progression from stigme (point) to gramme (line) to epipedon (plane) to stereon (solid) — the four dimensions of spatial reality — and simultaneously contains the harmonic ratios: the octave (2:1), the fifth (3:2), and the fourth (4:3). The Dekad that the Tetractys sums to represents teleion — cosmic completeness, the number in which all arithmetical relations find their fulfillment.

Cross-Tradition Resonances