Tetraktys

The tetractys was a triangle symbol held sacred by the Pythagoreans. It included all the numbers needed to describe the world. It also formed the basis for the Pythagorean musical system but it's also a representation of cosmic harmony. Matti Salo himself describes it as "a mathematical and metaphysical symbol through which all can be seen as coming into being".
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Salo has explored this symbol through his compositions and Tetraktys is an abstract concept album, with the story being left open for interpretation by every listener.