One of the mysteries about the pyramids is how such a primitive civilization in comparison to our modern civilization, was able to move massive slabs of limestone. One historians theory, may just be the most logical answer to this question.
The theory posed by Joseph Davidovits is that the Ancient Egyptians actually poured limestone concrete molds and the massive bricks were cast that way. Joseph believes that using the tools of the ancient Egyptians, water from the Nile, and a lengthy amount of time in the sun, the Egyptian workers were able to follow a simple process in order to create this massive bricks.
Basically, the limestone was broken down and mixed with water from the Nile, and left out until the mixture blended together. The mixture was then carried to the Pyramid and poured into a wooden mold, where it would then harden over the course of a few days.
Researchers tried to see if this was a realistic way to build the pyramid. A crew of 10 people in France, followed these exact steps proposed by Davidovits and it was found that over the course of a few weeks, the crew made a structure of 5 blocks, weighing anywhere between 1.3 - 4.5 ton blocks! Which means, we may have once and for all figured out how the Egyptians built the pyramids.