I remember seeing a video demonstration of how a single person can erect stones as in Stonehenge. Basically, you lever it up bit by bit by placing a log or b other fulcrum under the stone, off-center, and place weights on the shorter end until the other end of the stone lifts. Add a higher fulcrum on the other side, repeat until the stone is high enough to be tipped into a hole dug into the ground to hold it.