Interpreting the Black Pig’s Dyke

The Black Pig’s Dyke has twelve major sections of linear earthworks attributed to it. However, these portray such variability that they cannot be reduced to one interpretation. Of the twelve sections, just six— the Dunclá, Co. Longford; Ardkill More, Co. Cavan; the Worm Ditch, Co. Leitrim; the Black Pig’s Race, Co. Monaghan; the Dorsey, Co. Armagh; and the Dane’s Cast, Counties Armagh and Down —can properly be defined as linear earthworks. These are all a particular form of linear earthwork, distinguished by their large size, monumentality and morphological complexity, represented by multiple phases of remodelling and refurbishment.

The remaining sites, apart from Dowra, Co. Cavan (which is likely non-archaeological), and Maghernakill, Co. Monaghan (which may be a cursus monument*), are cut-off spurs formed by river meanders and are best interpreted as multiple bank and ditch defences for riverine promontory forts.

The earthworks at the Doon of Drumsna are especially interesting, due to their remarkable scale, extent and complexity, which appear to defend an enormous area of 188 hectares, far larger than any Irish hillfort). The Doon has out-turned entrances which are unique to Ireland, but common on large hillforts elsewhere in Europe. These, along with its siting on a major riverine trade route into a heartland of the Irish La Tène ‘province’, and suggestions from archaeological surveys of extensive late prehistoric – possibly Iron Age – activity ‘within’ its ramparts, all point towards the need for a reassessment of previous interpretations of the Doon as simply a barrier to protect a fording-point on the Shannon. Instead, perhaps the Doon of Drumsna should be considered as a unique Irish example of the type of large-scale riverine promontory fort that is found in the British and Continental Iron Age, for example at Villeneuve-Saint-Germain and Dyke Hills?

Up until the 1970s it was generally thought that the Irish linear earthworks newer than, and were influenced by Roman defensive barriers such as the Antonine Wall and Hadrian’s Wall. Thanks to the dating of the Dorsey and the Aghareagh West section of the Black Pig’s Dyke to the last centuries BCE, it has become commonplace to discount any possibility of a Roman influence on Irish linear earthworks. However, more recent analysis of that data suggests that their currency might well have extended between the fourth century BCE and the early third century CE, which would not preclude influences from the Roman world. Likewise, whilst the monuments most probably belong to an Iron Age horizon, it is not known exactly when they emerged and for how long they continued to be significant. A dating programme that is currently under way will assist in refining their chronology.

*A cursus monument is a monument made up of large parallel lengths of banks with external ditches. It gets its name from the Latin for “course”, as they were originally thought to be Roman athletic courses.

Traditionally, the earthworks were assumed to be defensive or a social, political or economic barrier to control the flow of people. But their monumental size and nature, as well as the enormous resources, in terms of materials and man-power, required to erect them were out of all proportion to any role they might have had for defence or control, or as boundaries that were intended to divide up an agricultural landscape.

The siting of the earthworks makes little military sense; their circuits seem to have little or no logic and are not easily defended in many locations. Early history fails to record them as having had a role in military encounters, and there is no evidence that they were integrated into an agricultural landscape. In fact, they appear to have had little or no practical purpose as boundaries or barriers.

So we look to other reasons for their existence, reasons that are more social or religious. One intriguing theory is that the great lines of ditches were created as ritual acts to inscribe messages about the power and supremacy of Celtic élites into the topography of contested landscapes. It was not the finished monument that was significant: it was the event of construction that mattered. The names of those who had the great linear earthworks built must have endured in memory for many generations, but were ultimately to be replaced by a folk story about a mystical Black Pig or a gigantic worm.