The Country Out Thar

I took the dog out for a walk up the hill today, and, as promised, brought back some pictures of the countryside around here. (See hovertext.)
Near the top of the hill, hidden in the high grass and covering trees, is the remnant of what was once a mighty wall, now in dire need of mending. For without a wall, how would I know what I am walling in, or walling out?