The Black Pig’s Dyke (Irish: Claí na Muice Duibhe) is a series of imposing but discontinuous earthwork barriers running from County Leitrim in the west to County Armagh in the east, broadly tracing the southern border of the ancient province of Ulster. Constructed probably in the late Iron Age to defend against cattle raids, the earthworks consist of a raised bank with ditches on either side, some sections still reaching several metres in depth and width. Remnants survive in County Leitrim, County Longford, County Cavan, County Monaghan, and County Fermanagh.
The story
The Gaelic folk tradition explaining the dykes exists in two main forms. In the most widely recorded version, a schoolmaster in Ulster ran a punishing and feared regime over his pupils; one of them, managing to get hold of the master’s hidden book of magic spells, transformed him into a vast and furious black pig. The maddened beast plunged through the countryside, its tusks ripping open the earth and throwing up the long embankments visible today as it ran. A second and older tradition gives the same earthworks to a colossal worm or serpent, and the Irish name Claí na Péiste (‘Worm’s Ditch’) preserves this alternative folklore.
The earthwork is documented on the 1837 Ordnance Survey of Ireland maps and has been examined in the Ulster Archaeological Journal and by field archaeologists. The dedicated heritage website blackpigsdyke.ie records the oral traditions associated with it, and the site is listed among Irish prehistoric monuments with significant attached mythology by Voices from the Dawn. The County Fermanagh sections of the dyke remain among the most visible, running through the townlands of Lislea and Mullynavannoge in the northwest of the county.