Magli showed that the choice of pyramid sites after Giza was determined by the setting points on the western horizon of bright Decanal stars as seen from Heliopolis, at nominal date 2500 BC –
The Heliopolis/Giza alignment pointed to the setting of a group of bright stars, the constellation Crux and Alpha Centauri, and also the brightest part of milky way. This was the target of the ‘Giza diagonal’ (correctly the diagonal running through the centre of Khafre – not the so-called ‘Giza diagonal’ almost touching the south east corners of the 3 large pyramids) –
The 45 degree diagonal at Giza
I have argued that the relation between the side and diagonal of a square represented a kind of metaphysical interpretation of geometry, and the 45 degree alignment from Heliopolis through Giza to this cluster of celestial objects might well have had great mythological meaning, now unfortunately lost.
The alignment from Heliopolis to Abu Rawash points to the setting of Sirius but also to the winter solstice sunset. Heliopolis was called the ‘city of the sun’, cult centre of the sun god Re, and its priests undoubtedly had full control over what might be termed ‘the Giza project’. At the natural entrance to the plateau the builders carved the Sphinx, boldly facing the rising sun. In the New kingdom the figure was called ReHorakhty – a syncretism of Re and Horus.
From the Sphinx the mid-winter sun is seen to set between the two large pyramids –
Akhet Khufu
This ‘hierophany’ has been compared to the hieroglyph Ahket (‘horizon’) of the sun between two hills (shown in colour). (This particular hieroglyph is not encountered until after Giza – perhaps Giza was a prototype). Whether Khufu and Khafre were primarily planned with this vision in mind (simply because of their sheer size), they emphasized it by the placing of the Sphinx complex, at the foot of the plateau, and echoing the alignment from Heliopolis to Abe Rawash and the setting of the midwinter sun.
The sloping rock glacis separating Khafre and the Sphinx is the ideal location for a causeway, but the same can hardly be said for Khufu. Yet both causeways appear to be ‘symmetrically’ laid out at around 14 degrees from due east. Bauval and Magli argued that this represented bisection of the extremes of solar azimuths (28 degrees) as an explanation, the causeways falling into alignment on dates of presumed ritual significance –
Causeways and solstices
The problem is that different angles are given in the literature for the causeways. Hassan assumed 14 degrees. The GPMP base map yields about 13.3 degrees. In the case of Khufu, Nell and Ruggles give 13 degrees 29’30” whereas Hawass has 14 degrees 46’56”. From survey data Butler estimated that Khafre causeway was laid out as the diagonal of a 1 X 4 rectangle.
Khafre’s valley complex fronted the principal harbour and from here the theophany represented by the midwinter sun setting between the two large pyramids is plain for all to see. Less obvious is the geometric alignment passing through the Sphinx at 30 degrees from the north west corner of the plan –
Sphinx alignment
Magli notes that the causeway of the Bent pyramid is also aligned to the winter solstice.