At the heart of Pythagorean philosophy is the triangular pattern of 10 dots or points called the 'tetractys'. Mathematicians regard it as the fourth of the so-called 'triangular numbers.' These are numbers that are the sums of triangular arrays of dots, each denoting the number 1. For example, 1, 1+2=3, 1+2+3=6 and 1+2+3+4=10 are the first four triangular numbers. The tetractys, however, meant far more than this to the followers of Pythagoras. In fact, so much did they honour it that they swore to their teacher, who had recognised the meaning and importance of this pattern, an oath of loyalty that mentioned the symbol. Just as the number 1 is the source of all number, so the Monad symbolized by a point or dot is the divine origin of all phenomena. Integers increase until they attain their perfect completion in the number 10, the Decad. The tetractys is more than just a representation of this number. It symbolizes the 10-fold nature of Divine Unity as it manifests in existence — physical and superphysical. As such, it is the template for constructing holistic objects that possess sacred geometry.

The tetractys is a set of four horizontal rows of 1, 2, 3 & 4 dots. The properties of objects possessing sacred geometry can be expressed naturally in terms of these four integers. Any dot which is part of a tetractys will be called a 'yod' because this is the name of the tenth letter (י) of the Hebrew alphabet, which is shaped somewhat like a dot.