Tetractys

The tetractys (Greek: τετρακτύς), or tetrad,^[1] or the tetractys of the decad^[2] 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.^[3]

^ The Theosophical Glossary, Forgotten Books, p. 302, ISBN 9781440073915
^ Eduard Zeller. Outlines of the History of Greek Philosophy (13 ed.). p. 36.
^ Dimitra Karamanides (2005), Pythagoras: pioneering mathematician and musical theorist of Ancient Greece, The Rosen Publishing Group, p. 65, ISBN 9781404205000

[1] The Theosophical Glossary, Forgotten Books, p. 302, ISBN 9781440073915

[2] Eduard Zeller. Outlines of the History of Greek Philosophy (13 ed.). p. 36.

[3] Dimitra Karamanides (2005), Pythagoras: pioneering mathematician and musical theorist of Ancient Greece, The Rosen Publishing Group, p. 65, ISBN 9781404205000

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