Quote from kairos:
I like the FACT that the ancient builders of the world's megaliths not only accomplished tasks still not attainable by modern technology, they also thought the earth was flat.
true story.
Some Bible scholars have come to believe that those builders possessed super-human skills and abilities. They may have been the Giant Nephilim who populated Earth in the time of Noah and later. If that is so then they would have known that Earth is indeed a spheroid.
It is quite true that our modern construction skills and machinery would not enable us to readily duplicate many of those ancient structures. One day we will know how they were made and who made them.