The "Tetraktys" was the symbol of the Pythagoreans, the philosophic (and musical) school linked to the almost mythological figure of Pythagoras of Samos.

Its image is an equilateral triangle based on the essential numbers 1 (top), 2, 3 and 4 (base), whose sum is the perfect number 10. These numbers were considered by the Pythagoreans to be holy and at the origins of the universe. Musically they represent the perfect consonants: the unison, the octave, the fifth and the fourth. The tuning used in the music of the Middle Ages, based on a succession of perfect fifths, is still called Pythagorean. The relationship between number, proportion, astronomy and music held a fascination for scientists (Keppler, Kircher, Fludd) and musicians (Bach) far beyond medieval times. The image, from Robert Fludd’s Philosophia Sacra, 1626, shows how the original absolute darkness preceded the Monad (1), the first created light. The Dyad (2) is the polarity of light (Lux) and darkness (Tenebrae), with which the Humid Spirit (Aqua) makes a third. The polarization of the four Elements (Ignis, Aer, Aqua, Terra) concludes the foundation of the world.

The Ensemble Tetraktys was founded by Kees Boeke in 2000 and has realized four CD recordings for the new label O-live Music : Trecento, as a duo with Jill Feldman (soprano) and Kees Boeke (flute and viella), and as a quartet, adding harp and a second viella, Dufay Chansons, works from the Squarcialupi Codex, works from the Chantilly Codex, Vol.1 (with Silvia Tecardi, viella - Marta Graziolino, harp and Carlos Mena, altus) and Vol.2 (forthcoming, with soprano Zsuzsi Toth and Carlos Mena, altus