>Suppose instead of avoiding hills on the route from the Downs to Salisbury plain Neolithic man used these hills in the same way that modern man uses the moon when sending satellites into deep space.<

That's an interesting idea Gordon but correct me if I'm wrong when I say that the sarsens for Stonehenge came (mostly?) from Piggledene, and the route from there to Stonehenge is mostly uphill (or on the level?). May have that completely wrong however.