Black Pig's Dyke

A notable example is the Claidh Dubh ("black ditch"), anglicised Clyduff or Cleeduff, in eastern County Cork.

[3][4] [5] In Counties Leitrim and Cavan, the earthworks are generally called the Black Pig's Dyke or Dike.

[6] Excavation of a stretch in County Monaghan revealed that the original construction was of a substantial timber palisade with external ditch.

[7][8] Such dates confound the once popular theory that the earthworks were made in imitation of the Roman frontier in northern Britain.

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.

According to Irish folklore, the earthworks were created by the tusks of a huge black boar
Depiction of a cattle raid in 16th century Gaelic Ireland – it is believed that the earthworks were built to prevent such raids