Not saying it was Aliens. Geologists stated on more than one occasion that the Sphinx is much older. Dating back to, maybe even prior the last ice age. There was most likely another human civilization before the Egyptians. Just look at all those ancient buildings all over the world that somehow seem to be linked in style, architecture, technique, age or the astronomical mathematics involved. We built on top of them, used what was left.
We, the modern human, is like 200.000 years old. For 195.000 years nothing happened and then all of a sudden we started building pyramids or other megalithic structures? We went from hunting and gathering to sending men on the moon in 5.000 years, but for 195.000 years nothing happened?
But we did do a crapton in that time. We developed, in no particular order: fishing, art, clothing, domesticating animals, spread all over the planet, farming, domesticating plants, currency, pottery, weaving, jewellery, pigments, belief systems, music, astrology, construction, writing, developed new and better and more specialised tools, war, hearths, metallurgy, architecture and probably some other stuff I forgot!... All before those 5000 years. Heck you can even squeeze in urbanisation, mathematics, social hierarchies, and probably some other things I forgot.
Sweet mother of mercy we did a LOT during that time period, including building megalithic structures for thousands of years before the last 5000. Just look at our closest cousins, they aren't even close to the level we were at 200000 years ago. Now I agree that the Sphinx still has a lot of mysteries we don't know, and might never know. And thats cool, we all have our secrets. But we certainly did not go "from hunting and gathering to sending men on the moon in 5.000 years."
The dogma must remain, no matter the proof.
But what proof do you have? There are a few fringe theories that I know of (my neighbour likes to share them a lot, though he believes the great flood wiped out the complex civilisation of the Atlanteans and that we had to start over again after that) but we know ancient peoples (certainly within the last 5000 years) were steadily developing complex mathematics needed to build these kinds of buildings. And they had the knowledge of the stars to align them.
So yes, who else had built the pyramids, since they clearly developed faster then we did if they had the capability to do so before the Egyptians.