The Ennead of Heliopolis organizes the beginning of the world into a strict three-generation family tree, the clearest genealogical creation account to survive from ancient Egypt. Atum, self-created from the primeval waters of Nun, either by masturbation or by spitting depending on the version of the myth, produces the first pair, Shu, air, and Tefnut, moisture, without any partner.
Shu and Tefnut in turn produce Geb, the earth, and Nut, the sky, whom Shu is depicted physically separating by standing between them, holding Nut's star-covered body aloft above Geb's reclining form, one of the most immediately recognizable images in all Egyptian religious art. Geb and Nut then produce the final and most narratively active generation, the two divine couples Osiris and Isis, and Set and Nephthys, whose story of murder, dismemberment, magical restoration and rightful kingship supplies most of what a general reader knows of Egyptian myth at all. The number nine mattered enough in its own right that Egyptian temples elsewhere adopted the same organizing device for their own local pantheons, an Ogdoad of eight at Hermopolis, other groups elsewhere, showing that the Ennead was as much a theological template, a way of organizing any set of locally important gods into a family structure, as it was a fixed list bound only to Heliopolis.