In Ancient Egypt the Legend of Osiris was so important that it was integrated into the solar theology. As a result Isis and Nephthys, the two mourners of Osiris, became an essential part of some solar iconography, so both from the New Kingdom were depicted flanking the solar disk in its daily rebirth.
It also had an effect in the holy conception of geography in Ancient Egypt. If the rising sun occupied the east and the sunset the west, the two mourning goddesses had to be also located somewhere, so they had to have also a geographical assignation: north and south. At that point the titles of the two goddesses are quite explicit. In Ancient Egypt, Isis was “The One of the South” and Nephthys “The One of the North”.