As seen in other images in this set, the dry stone wall follows the line of the ridge (and the Cumbria / North Yorkshire county boundary) for several kilometres. At the summit, a couple of metres from the triangulation pillar, an elegantly-curving spur has been added on each side of the wall to serve as a sheltered rest point.
This is the western, Cumbrian side seen from an unusually high viewpoint – I was standing on the trig pillar.