Black Pig's Dyke

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The Black Pig's Dyke (Irish: Claí na Muice Duibhe)[1] is a series of discontinuous linear earthworks in south-western Ulster and north-eastern Connaught, across the width of Ireland. It is also known as the Worm's Ditch (Irish: Claí na Péiste)[1]

Remnants of the Dyke can be found in the north of the counties of Leitrim and Longford, and running through the counties of Cavan, Monaghan and Fermanagh, the latter in the United Kingdom. Sometimes, the Dorsey Ramparts in Armagh and the Dane's Cast in Downshire are considered to be part of the dyke.

Similar earthworks can be found throughout Ireland,[2] but the Black Pig's Dyke is the best known and best celebrated in legend. It has three sections, the longest of which runs north to south for 15 miles from the Ballyhoura Hills to the Nagle Mountains.[3]


In the counties of Leitrim and Cavan the earthworks are generally called the Black Pig's Dyke or Dike. In County Longford it is called the Black Pig's Race, while in the Cavan–Monaghan border area it is called Black Pig's Dyke or Worm Ditch.

The ditches take their names from Gaelic folklore. One tale says that a huge black boar tore up the countryside with its large tusks. Another says that the ditches were made by a huge worm.

Construction and purpose

A depiction of a cattle raid in 16th century Gaelic Ireland

The earthworks usually consist of a bank with a ditch on either side. The bank is usually about 30 feet wide and the ditches are usually about 20 feet deep.[4]

Excavation of a stretch in County Monaghan revealed that the original construction was of a substantial timber palisade with external ditch. Behind the palisade was a double bank with intervening ditch. The timber structure was radiocarbon-dated to 390–370 BC, so all of the earthworks are assumed date to that period.[5] Such dates confound the once popular theory that the earthworks were made in imitation of the Roman frontier in northern Britain.[6][7]

Some have put forward the idea that the earthworks marked the ancient border of Ulster. However, there is no evidence that they "collectively constitute one border for one people" – the earthworks may not be contemporary and there are large gaps between them.[8] Others suggest that their sole purpose was to prevent cattle raiding, which was very common in ancient Ireland. Two theories have been put forward to explain why there are large gaps between the earthworks. One is that they were simply built across trackways that were often used by cattle raiders, another is that the gaps between them were once heavily wooded and thus no manmade defence was needed.[9]


The remains of the earthworks can be found in the following places:

  • North County Leitrim: running north-west to south-east, from Lough Melvin to Lough MacNean, near the villages of Rossinver and Kiltyclogher.[4]
  • North-east County Longford: running north-west to south-east for six miles, from Lough Gowna to Lough Kinale (crossing the N55), near the villages of Dring and Granard.[4]
  • County Cavan–County Monaghan border: running roughly west–east from the Finn River (near the village of Redhills) to the townland of Corrinshigo (near the village of Drum).
  • County Cavan: forming a wide semi-circle in the townland of Ardkill More, 3½ miles east of Bellananagh. This is one of the best surviving examples. > Cavan Heritage Group have called for the cessation of operations on a nearby quarry which they maintain is damaging part of the dyke at Ardkill More.[10]
  • County Fermanagh: part of linear earthwork, in Lislea townland (H48362706) and in Mullynavannoge townland, (H48382631 – H48502590) – Scheduled Historic Monuments[11]


  1. 1.0 1.1 Black Pig's Dyke: Foras na Irish and Dublin City University
  2. The Early Development of Irish Society. Cambridge University Press, 1969. pp.88–89
  3. Eachtra Journal: Issue 10. p.11
  4. 4.0 4.1 4.2 Antiquities of the Irish Countryside
  5. J. T. Koch, An Atlas for Celtic Studies (2007), p. 110 and map 14.1; J. Waddell, The Prehistoric Archaeology of Ireland (1998).
  6. Aidan Walsh, Excavation at the Black Pig's Dyke, Clogher Record, Vol. 14, No. 1 (1991), pp. 9-26.
  7. Walsh, Aidan. "Excavation at the Black Pig's Dyke". Clogher Record (Clogher Historical Society) 14 (1): 9–26. 
  8. Ireland: An Oxford archaeological guide to sites from earliest times to AD 1600. Oxford University Press, 2006. p.155
  9. Ireland: An Oxford archaeological guide to sites from earliest times to AD 1600. Oxford University Press, 2006. p.155.
  10. Indymedia Ireland
  11. Scheduled Historic Monuments, 1 April 2019: Historic Environment Division, DoCNI