The use of a trio of witches is quite common in literature and lore. Greek, Slavic, and British tales have used them as antagonists or catalysts in their (sometimes cautionary) stories. In other sociological constructs, such as pagan and wiccan religions, their qualities and form (maiden, mother, and crone) are often revered.
I'm curious to know if the Three Witches from Macbeth share a common origin with other similar people/creatures such as the Stygian Witches or The GraeaeStygian Witches or The Graeae.