Stonehenge

How did they build it? Dragging big stones around is hard and leaves traces, so there must have been an easier way to move them (sometimes 200 miles!). Two "new" ideas are that they created wicker cradles to roll them in, and that they used stone balls as ball bearings in wooden troughs to make it easier. The latter method has some obvious problems when dragging rocks uphill, but they don't seem insurmountable. It should be possible to try to verify the method. Some fraction of the stone balls should have spalled and become unusable, so they should look for marred balls in among the rest. Oak balls or roller dowels don't last so long, unfortunately.