Answer: If you visit the desert, you will find Great, Naturally Created Giant Stones in the shape of a Pyramid. The action of sand on Stone, a genuine “sandblasting” over eons turns Solid Stone into a Pyramidal shape. The winds and Sandstorms create these without help of man. So I have long believed that since the Ancient Egyptians must have seen this natural phenomena, they chose that ideal Particular Shape because it would, over the ages, maintain its general, original Pyramidal shape. These were a people who planned ahead; even the poor who died saved “essentials” for the Afterlife as they saw it. As much work and planning, and manpower as it would take to build the Ultimate Monument to a “living god” until they reached the next level as they saw it; it MUST be a confirmation that will last! What better model to follow than to see Nature does prefer a Pyramid. The Pyramids of Giza look less than ideal because of thousands of years of theft of Stone; the original White Limestone covering, must have been stunning! It was not to be; their civilization and their “control” over the Pyramids was lost long, long ago. The Pyramids still do look like “Pyramids” even if people have stolen and damaged them. So, it appears to me that the Ancients, who watched the Stars and Heavens, did look at Nature around them, and they saw - Pyramids of Stone of great antiquity.
The reason that they have done this (this is a theory created by Egyptologists) is so the dead pharaoh could symbolically climb the sides of the pyramid, make his way to the sky, and live forever. The pyramid also represented the rays of the sun.