The Claidh Dubh is a linear earthwork running for a distance of 22 kilometres (14 miles) across the Blackwater Valley in North Cork. The entire earthwork was surveyed, 800m of which was surveyed in close detail. Limited excavation was also carried out on a section in the Nagles Mountains. The purpose of the excavation was to examine the construction of the earthwork and to attempt to retrieve dating evidence. This work has shown that the earthwork varies considerably along its length, such as in the number of positions of the ditches and the height and nature of the bank. In places, shallow ditches flanked the bank which consisted of rubble. Parallel to the bank, on the eastern side and seemingly contemporary with it, was a surfaced trackway. Dates are uncertain, but the one Carbon 14 date retrieved indicates that a growth of peat had formed over the trackway by 100 A.D. It may well be, therefore, that both earthwork and track date from Iron Age times. Similar earthworks are known from other parts of Ireland, such as the Dorsey in Co. Armagh and the Black Pig's Dyke, which runs across much of Ulster. These seem to date from much the same period as the Claidh Dubh and appear to have acted as frontier defences of emerging or established northern kingdoms. The Claidh Dubh may be another such frontier boundary.
