The gods which personify the sun and sky stand apart in their essential idea from those already described, although they were largely mixed and combined with other classes of gods. So much did this mixture pervade all the later views that some writers have seen nothing but varying forms of sun-worship in Egyptian religion. It will have been noticed however in the previous chapters what a large body of theology was entirely apart from the sun-worship, while here we treat the latter as separate from the other elements with which it was more or less combined. _Ra_ was the great sun-god, to whom every king pledged himself, by adopting on his accession a motto-title embodying the god's name, such as _Ra-men-kau_, 'Ra established the kas,' _Ra-sehotep-ab_, 'Ra satisfies the heart,' _Ra-neb-maat_, 'Ra is the lord of truth'; and these titles were those by {51} which the king was best known ever after. This devotion was not primitive, but began in the fourth dynasty, and was established by the fifth dynasty being called sons of Ra, and every later king having the title 'son of Ra' before his name. The obelisk was the emblem of Ra, and in the fifth dynasty a great obelisk temple was built in his honour at Abusir, followed also by others. Heliopolis was the centre of his worship, where Senusert I, in the twelfth dynasty, rebuilt the temple and erected the obelisks, one of which is still standing. But Ra was preceded there by another sun-god Atmu, who was the true god of the nome; and Ra, though worshipped throughout the land, was not the aboriginal god of any city. In Heliopolis he was attached to Atmu, at Thebes attached to Amen. These facts point to Ra having been introduced into Egypt by a conquering people, after the theologic settlement of the whole land. There are many suggestions that the Ra worshippers came in from Asia, and established their rule at Heliopolis. The title of the ruler of that place was the _heq_, a Semitic title; and the _heq_ sceptre was the sacred treasure of the temple. The 'spirits of Heliopolis' were specially honoured, an idea more Babylonian than Egyptian. This city was a centre of literary {52} learning and of theologic theorising which was unknown elsewhere in Egypt, but familiar in Mesopotamia. A conical stone was the embodiment of the god at Heliopolis, as in Syria. _On_, the native name of Heliopolis, occurs twice in Syria, as well as other cities named Heliopolis there in later times. The view of an early Semitic principate of Heliopolis, before the dynastic age, would unify all of these facts: and the advance of Ra worship in the fifth dynasty would be due to a revival of the influence of the eastern Delta at that time.