Pythagoras, as one example among many, believed that the number 12 was the number of the universe, insofar as "the universe" is understood as the yoking of the 1 (God) to the 2 (creation-- the variegated expression of the 1). You find a similar concept in the I Ching, where the first two hexagrams are related to the yang (1) and the yin (2).
