I wonder if they erected the (probable) stone pair at the one end of it?

I actually went to check out two stones I could see from Castleruddery stone circle and found that they stood at the end of this huge ditch. The stones are eratics, but have been stood up so that their pointy end is upmost and they are set to align on a significant notch in the surrounding mountains. I'm amazed they have never been moved (although someone has tried to break one of them up) because they actually stand in what would be a natural gateway between two fields.

This little arrangement is just 300m from the circle and set above a field where local lore has bull fights used to take place. One side of this field is circular! The slope down to this field is terraced as if to provide viewing platforms above the field. Castleruddery itself is an embanked enclosure set within a 100m diameter henge (now only visible as a slight bump in the ground and on aerial photos.)