It appears that the Great Pyramid of Giza was never finished since the top is flat, and not pointed, as it should be. It has a truncated summit which is coarse and uneven and measures about 30 square feet. Most pyramids were crowned with a top-stone that completed their structure. This pyramid does not currently have one and it appears that it never did. One of the earliest references to the missing top-stone (or capstone) is from Diodorus Siculus (60 BC).
Diodorus tells us that in his day, when the Pyramid stood with its casing stones intact, the structure was "complete and without the least decay, and yet it lacked its apex stone.” Since the top-stone could not have been dismantled without first demolishing the smooth casing-stones, so that the core masonry formed steps of approach to it, this statement of Diodorus supports the theory that the top-stone had never been added to the structure.
Also it appears that between the different courses of stones there is a thin cement which is absent on the upper surface of the highest course. Why the pyramid capstone is missing remains a mystery to the world.