2. Memphis (possibly also Saïs, Bubastis, Tanis and other cities with east and west walls) and the great pyramids were built by a new invading race, representing an advance in astronomical thought. The northern stars were worshipped possibly on the meridian, and a star rising in the east was worshipped at each equinox. 3. The subsequent blank in Egyptian history was associated with conflicts between these and other races, which were ended by the victory of the representatives of the old worship of Annu, reinforced from the south, as if north-star and south-star cults had combined against the equinoctial cult. [Illustration: MNEVIS.] After these conflicts, east and west pyramid building practically ceased, Memphis takes second place, and Thebes, a southern Annu, so far as the form of solar worship and the cult of Sit are concerned, comes upon the scene as the seat of the twelfth dynasty.[103] 4. The subsequent historical events were largely due to conflicts with intruding races from the north-east. The intruders established themselves in cities with east and west walls, and were on each occasion driven out by solstitial solar worshippers who founded dynasties (eighteenth and twenty-fifth) at Thebes. [Illustration: THE TWO GREAT PYRAMIDS AT THE TIME OF THE INUNDATION.] Some detailed remarks are necessary on several points connected with the above generalisation. I will take them _seriatim_. We find at Memphis, Saïs, Bubastis, and Tanis, east and west walls which at once stamp those cities as differing in origin from Annu, Abydos and Thebes, where, as I have shown, the walls trend either north-west--south-east or north-east--south-west. For Memphis, Saïs and Tanis the evidence is afforded by the maps of Lepsius. For Bubastis it depends upon the statement of Naville, that the walls run "nearly from east to west," and with the looseness too often associated with such statements, it is not said whether this bearing is true or magnetic. Associated with these east and west walls there is, moreover, evidence of great antiquity. Bubastis, according to Naville,[104] has afforded traces of the date of Cheops and Chephren, and it is stated by Manetho to have existed as early as the second dynasty. It is a matter of common knowledge that the pyramids in Egypt are generally oriented east and west.[105] Nor is this all; there has been a distinct evolution in their method of structure. One of the oldest, if not the oldest pyramid known is the so-called "step-pyramid of Sakkarah." The steps are six in number, and vary in height from thirty-eight to twenty-nine feet, their width being about six feet. The dimensions are (352 north and south) × (390 east and west) × 197 feet. Some authorities think this pyramid was erected in the first dynasty by the fourth king (Nenephes of Manetho, Ata of the tablet of Abydos). The arrangement of chambers in this pyramid is quite special. [Illustration: THE STEP-PYRAMID OF SAKKARAH.]