What little remains of it carries a name that tells you something about how local memory works: 'the Gripe of the Pig', a gripe being a drainage ditch or trench, and the pig in question a very particular animal indeed.

The earthwork is recorded as 'Rathduff Trench' on an early seventeenth-century barony map of Idrone, published by Gerard Mercator between 1606 and 1641, where it marks the north-western boundary of the Carlow barony at a time when that barony extended into territory that is now county Kilkenny. By 1839, when the Ordnance Survey letters were compiled, it had already been nearly erased by cultivation; the surveyor noted that only fragments and associated ringforts, if mapped, would preserve its outline. The local tradition recorded at that time linked it to the Black Pig's Dyke, a class of large boundary earthwork found elsewhere in Ireland and generally associated with early medieval territorial divisions, though the precise date and purpose of the Rathduff Trench remain unknown. The legend offered to explain the name was more domestic in character: a poor widow's pig escaped into an underground passage, and the neighbours who dug after her, all the way down to the Barrow, left behind both the trench and the spoil heap on its bank. Archaeological excavations carried out ahead of the Cork-Dublin gas pipeline in 1981 and 1982 confirmed the earthwork's basic form in Shankill townland, a low bank roughly 0.7 metres high beside a fosse, the fosse being the ditch on the southern side. What those excavations also revealed was that the fosse had been substantially recut in 1954 by the Land Commission as part of a drainage scheme, obscuring much of the original profile. The original fosse had been considerably more substantial, around five metres wide and just under a metre deep, but no datable material was recovered to establish when it was first constructed.

The area around Kellymount, on the south-eastern edge of the Castlecomer Plateau, is noted as the place where the trench is still faintly traceable, though additional stretches were identified east of the railway line within Shankill Castle demesne, running on a slightly different axis. The earthwork is the kind of feature that rewards patience rather than spectacle; most of it is gone, and what survives is subtle, its interest lying less in what can be seen than in the long argument between landscape, legend, and the persistent fact of a boundary that someone, at some point, thought worth digging.