But it was not as Tum that the sun-god of Heliopolis thus made his way victoriously through the land of Egypt. It was under the more general and undefined name of Ra that he was accepted in the Egyptian sanctuaries. Tum remained the local god of Heliopolis, or else formed part of a solar trinity in which he represented the setting sun. But Ra became a divine Pharaoh, in whom the world of the gods was unified.
The kings of the Fifth Dynasty called themselves his sons. Hitherto the Pharaohs had been incarnations of the sun-god, like the earlier monarchs of Babylonia; henceforward the title of Horus was restricted to their doubles in the other world, while that of "Son of the Sun" was prefixed to the birth-name which they bore on earth. The same change took place also in Babylonia. There it was due to the invasion of foreign barbarians, and the establishment of a foreign dynasty at Babylon, where the priests refused to acknowledge the legitimacy of a king who had not been adopted as son by the sun-god Bel-Merodach. Perhaps a similar cause was at work in Egypt. The Fifth Dynasty came from Elephantinê, an island which was not only on the extreme frontier of Egypt, but was inhabited then as now by a non-Egyptian race; it may be that the price of their acknowledgment by the priests and princes of Memphis was their acceptance of the title of "Son of Ra." It narrowed their pretensions to divinity, and at the same time implied their submission to the god of the great sanctuary which stood in such close relations with Memphis. As we have seen, the first monument on which the winged solar disc is found is that of a king of the Fifth Dynasty; it there overshadows his figure and his two names; but though the hawk of Horus stands above the name of his double, his birth-name is without the title of "Son of Ra."
When once the principle had been adopted that the leading gods of Egypt were but varying forms of the sun-god, it was easy to construct Enneads, whatever might be the number of the deities it was wished to bring into them. Thus at Heliopolis itself Horus the son of Isis was introduced, his confusion with the sun-god Horus facilitating the process. At This, Anher was identified with Shu; at Thebes, Amon was made one with Tum and Ra, with Mentu and Mut. Where a goddess was at the head of the local Pantheon the process was the same; she interchanged with the other goddesses of the country, and even with Tum himself. At all events, Horapollo (i. 12) states that Nit of Sais was at once male and female.