An Cliadh Dubh runs between the Nagle and Ballyhoura mountains for some sixteen miles, or, by some accounts from Youghal in county Cork to Tarbert in county Kerry. A recent archaeological excavation of a section of the Cliadh Dubh suggested that it was built to defend against attack from the west, possibly by wolves.It is believed to exist since at least 100 AD. In English it is usually referred to as the “Black Ditch” but the direct translation of Cliadh Dubh is “Black Boar” and legend suggests that a huge black boar tore-up the countryside with its large tusks. If you want an even more exotic explanation there is a story that it was made by a huge worm!
Here, on both sides, it just looks like a little bit of overgrown ground between sections of forestry but is more prominent further up the mountain.