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(Lehner, Complete Pyramids, 1997, 106-7)

Any overview of these colossal human achievements in stone must take into consideration the natural geology of the land they were built on. The southeast corners of the pyramids of Khufu, Khafre and Menkaure are nearly aligned on the great Giza Diagonal that runs about 43° east of true north, almost perpendicular to the dip of the plateau. This follows what geologists call the strike of the Mokattam Formation, that is, a line perpendicular to the slope. When you walk along a hill without going up or down, you are following its strike. By aligning themselves to this, the builders ensured that the bases of the three main pyramids were at approximately the same level, although the base of Khafre’s is about 10m (33 ft) higher than Khufu’s.

Some religious or cosmic impulse beyond the purely practical may also have influenced the builders, although we can only speculate what it was. Perhaps the diagonal pointed northeast to Heliopolis, the home of the ben-ben, and southwest, in the direction of the Netherworld entrance of the first royal cemetery at Abydos.

… The formal symmetry of the pyramid complexes at Giza inspires many pyramid enthusiasts to look for more alignments, always with the suspicion of hidden meanings or lost treasures. A theory of Robert Bauval suggests that the Giza diagonal is inspired by the stars in the belt of the constellation Orion, which the Egyptians saw as a symbol of Osiris. Bugt when the map of Orion is positioned over that of Giza and nearby pyramids, it is clear that there are stars in Orion for which there are no matching pyramids, and pyramids for which there are no stars in Orion, or any other constellation.