I would like to continue along the lines of benign.psychosis.
Below is an systematic explanation of how the pyramids were built. I do not want to get into great detail (that would take many posts!) I will provide
summary facts. Please read this before simply concluding 'the aliens built them'.
It is first important to mention the 3rd dynasty step pyramid created supposedly by Djoser.
This pyramid was built in stages:
It started off as a mastaba tomb, a common 1st and 2nd dynasty royal tomb.
It was then enlarged and the three smaller mastabas were built on top to make it a 4 step pryramid.
Then it was enlarged further and two more steps were built on top to make it a 6 stepped pyramid.
- See the picture with the different stages of building highlighted:
Other step pyramids were built after Djsoer in Dynasty 3, such as Sekhemkhet's (which wasn’t finished) and the pyramid at Zawiyet el-Aryan using
the blue prints learnt from the construction of Djoser’s pyramid.
Then come the Dynasty 4 pyramids.
Snefru built the 'bent' pyramid at Dahshur, a time of continuing experimentation with pyramid building, as is evident with how the pyramid turned
out.
The pyramid was built with 60 degree angles but was too steep and therefore the pyramid was enlarged to lessen the angle. Problems still occurred and
about half way the masons changed the building technique due these problems so the sides slope decreased somewhat, which gives the pyramid its bend.
Snefru's other pyramid at Meduim was built in stages. It was first a stepped pyramid (like Djosers, but with much better engineering and a steeper
angle). It was then covered and faced to become a true pyramid. Although today only part of the stepped construction remains.
-see the picture with different stages of construction:
Snefru then built the 'red' pyramid at Dashur. Learning from the mistakes of the bent pyramid, the masons built the pyramid at a gentler slope and
by this time had a good plan of how to construct the pyramid.
Thus by Khufu's time (who build the great pyramid at Giza), nearly 100 years after Djoser's Step pyramid, the masons in Egypt had a blue print of
how a pyramid should be built, they had enough experience and expertise with building pyramids that they could build Khufu's 'great' pyramid at
Giza.
Through the above explanation I hope you see how the true pyramid 'evolved' through the Egyptian 3rd-4th dynasties. With such an evolution from
Djosers pyramid to Khufu's and looking at the pyramids in between, it is very doubtful the pyramids were anything other then man-made because of the
stages and experimentation the pyramid went through over these two dynasties to become what you see at Giza. If the aliens did build them, then why
did it take so many pyramids to get it right? Sounds like human experimentation in building technique to me!