Definition:Tetractys

Definition

The tetractys is a central concept in the mystical beliefs of the Pythagoreans.

It consists of $10$ points arranged in a triangle:

based on the notions that:

$1$ represents the point
$2$ represents the line
$3$ represents the surface
$4$ represents the solid
$1 + 2 + 3 + 4 = 10$

and therefore:

$10$ represents the universe.

Also known as

Some sources give this as tetraktys.