Written between 1962 and 1968, Campbell's four-volume work The Masks of God covers mythology from around the world, from ancient to modern. Where The Hero with a Thousand Faces focused on the commonality of mythology (the "elementary ideas"), the Masks of God books focus upon historical and cultural variations the monomyth takes on (the "folk ideas"). In other words, where The Hero with a Thousand Faces draws perhaps more from psychology, the Masks of God books draw more from anthropology and history. The four volumes of Masks of God are as follows: Primitive Mythology, Oriental Mythology, Occidental Mythology, and Creative Mythology.