I just find it difficult to believe that all the land between Stonehenge and the west of Wales was pasture. The way I see it is - You would have dense mature woodland, light woodland, brushwood, pasture and cultivated land..

Only pasture is relatively easy...

But lets not forget natural features like gully's and ditches..

I haven't looked, so I have no idea how many brooks, streams and rivers need to be crossed. How much swamp or marshland need to be circumnavigated..

Tony