Among many other things, they were most probably used to pump drinking water to public fountains in cities above the flood plain! This was accomplished by having a gigantic ram water pump inside the base of the pyramid. Configuration and dimensions of the inner chambers could reasonably mean little else....

The entrance to the Great Pyramid is 49 feet above the base. As an intake for the drive pipe for a ram pump, why was it put so high? Well, besides the fact that we're not really sure of the level of the water source back when the pump was operational, most likely it was simply for protection. The source was likely ancient Lake Moeris, in the nearby Libyan Desert, now dried up. The aqueduct feeding water to the pump would need to be elevated for protection from blowing, shifting sand as well as debris, animals or people. There would be a considerable amount of suction at this intake, and debris of any kind would threaten the operation of the pump if drawn in. There was certainly a strainer, filter or sieve of some kind to prevent this--perhaps a thin slab of stone with many holes drilled through it was placed in front of the entrance or intake hole. You can see that the hole was recessed into a rather large alcove-like area. This was probably an area reserved for periodic maintenence, protected from the outside. Perhaps here silt and debris was removed, with a stone gate to shut off the water supply for more thorough cleaning or even a shutdown of the pump.
|