The second name is the more widely recognised. The Black Pig's Dyke is a series of disconnected linear earthworks that once ran, in segments, across the northern midlands of Ireland, broadly tracing the ancient frontier between Ulster and the rest of the island. The name derives from a folk legend in which a monstrous black pig rooted its way through the land, leaving the trench behind it. What actually created it was human labour, probably during the Iron Age, though the precise date and purpose of individual sections remain contested.

This particular section is oriented north to south and consists of a flat-bottomed fosse, the term for a defensive ditch, measuring around three metres wide and up to about 0.6 metres deep in its more modest stretches, and considerably more pronounced where naturally lower ground to the east amplifies the profile, with the ditch top reaching 6.5 metres across and depths of between one and 1.6 metres. In some places a field bank survives along the outer, eastern edge of the fosse. The northern end of this section runs out at the south bank of the Lattone stream, where a flat-bottomed valley interrupts it, though separate recorded sections continue both to the north and, beyond Lough Tiernan, a small oval lake lying roughly 300 metres to the south-east, to the south-west. Much of it is now overgrown with scrub, and in parts it passes through coniferous plantation, where it was left unplanted but has grown dense with vegetation nonetheless. It is a National Monument in state ownership.