I think to believe we have any reliable understanding of ancient civilizations and the like is naive.
Follow me here...
There's sort of a desert belt around the earth - sw, c north america, north/most of africa, mid east, curving south to austrailia. Shouldnt these areas be plush, green, and teeming with life according to their latitudinal positions?
Consider the possibility that someone had taken issue with the ancient peoples for one reason or another and decided they were unfit for existence and adopted a "scorched earth policy". Perhaps some type of beam was fired from outside the atmosphere, descimatiing all it contacted. It may have started in sw america and followed the easerly route alluded to above. Ending up in austrailia, leaving behind nothing but the huge hole in the ozone which was left by the beam and a bunch of sandy earth (and some formidable stone structures).

The Dutch new stated earlier this week that Stone Henge was 300 years younger than we had believed till now.

The number of scelletons they found showing ilnesses would imply that Stone Henge was seen as "healing" place in that time

Perhaps these heavy stones of the pyramids and stone henge were moved with the "Law of Sympathetic Vibration". Anything is possible.

the egyptians ...levitated the huge stones for the pyramid by bouyancy .....lol in water...just like when when go swimming and we lift a heavy person in water its alot lighter. water also gives the ability to naturally be a actual leveling tool because of gravity. they flooded the inside of the pyramid when constructing and then just needed to build a water locks from the ancient lake moeris that was right next to the pyramid in ancient times to transport the blocks and also connecting to the nile etc depending on what area the blocks came from. lets not forget that there was found 4 boats on each cardinal point of the great pyramid because there was also a moat around the great pyramid possibly after constructing evident by the remaining wall that was never plundered for its stone for other buildings in the area.

Ok, here is a list of possibilities, from most possible to least possible, but still possible.
Pully system
Lots of people
Lots of people with the technology of aliens
Aliens
Supernatural(Possibility is 0)