The Parthenon is a special case in that, the more I learn about its structure, the more I ask that same question: How did they do it? Superficially, the great Athenian sanctuary appears to be quite regular from a geometrical viewpoint: nothing but a parallel series of vertical columns supporting a horizontal superstructure. But this is a gigantic illusion. When everything is measured, we learn with astonishment that there are no straight parallel lines whatsoever in the Parthenon. Everything is curved, often enormously. And the raison d'être of this curved design is to create the optical illusion of linearity, straightness and parallelism. In other words, if the stones were really straight, they would look curved. So, they've been deliberately curved by the architect in order to create the impression that they are straight.
Stonehenge, at first sight, is the sort of construction that tempts many folk to wonder whether it might have been built with help from the magical powers of Druids, or maybe even extraterrestrial giants. Finally, however, it's not too difficult to imagine ways in which the giant blocks might have been transported and then raised into their vertical positions.
No doubt the biggest construction mystery of all time has concerned the Great Pyramid of Giza... which happens to be the only one of the ancient Seven Wonders of the World that still exists.
Well, a former French architect named Jean-Pierre Houdin, with no specialized training in Egyptology, has just invented a revolutionary theory according to which the construction of the pyramid would have involved an internal ramp whose linear segments would have emerged into an open platform at each edge of the ascending pyramid, enabling a block to be turned and lifted onto the next segment of the ramp.
Houdin performed his calculations and computer modeling using resources supplied by the hi-tech company Dassault Systèmes. The following video gives you a good idea of the construction techniques imagined by Houdin:
As strange as it might seem, we can say retrospectively that, up until this theory was invented, the construction of the Great Pyramid of Giza had simply remained a total mystery. One might conclude that humanity seems to get along quite well without having to find answers to the question: How did they do it?
ADDENDUM: I've just finished reading an excellent book on Jean-Pierre Houdin's theory of the construction of the Great Pyramid. Coauthored by the celebrated US Egyptologist Bob Brier, the book is available from Amazon either in English or in French.
I bought the French version, because I wanted to read the preface by the French TV personality and intellectual François de Closets, who actually played a role in publicizing this huge breakthrough in our knowledge of the ancient world.