People in this thread act as if the Romans were baboons.

No, people 4000 years ago were still people, i.e. they had roughly the same brains as we do. This means their creativity and intellect was pretty much the same as we have now; they were more than capable of inventing techniques to carve and move large rocks. They didn't have modern technology, but they still had technology.

Also, building stuff by piling up rocks is so basic, it's normal that it evolved in parallel on different continents. OP's pic actually shows a few different solutions to the problem; some of them make neat rows while others are more "random" in their approach.