The Pentagram
No one knows the exact magical origins of the pentagram.... For centuries the 5 pointed star has been used as a symbol of protections and as a talisman for health and well being. It was popular among the Babylonians, Egyptians, Asyrians and Hebrews. According to Eliphas Levi, magicians of ole used to draw the symbol upon their doorstep, to keep malevolent spirits out and beneficent spirits in. And as early as the 6th century B.C.E. Pythagoras, the greek philosopher mystic, used the pentagram as a holy symbol for his followers. Five was the number peculiarity associated with the ideas of marriage and union, as it is the first number beyond the monad formed from the union of the first odd number and even numbers, male and female. It is also used to represent the human figure, with arms and legs outstretched. 
- Israel Regardie, The Middle Pillar