When construction of the N5 Swinford bypass was planned in the early 1990s, archaeologists moved in ahead of the machinery and excavated a rath near Lislackagh in County Mayo. A rath is a roughly circular enclosure, typically defined by an earthen bank and ditch, used as a farmstead or settlement during the early medieval period. What the excavation revealed inside, however, was considerably older than the rath itself.

In the western half of the enclosure, excavations carried out in 1992 and 1993 uncovered a circular house defined by a foundation trench, with an internal diameter of between 3.5 and 4 metres. No floor surface had survived the centuries, but charcoal recovered from the trench appeared to represent the burnt remnants of the structural timbers that had once formed the walls or roof. Radiocarbon analysis of that charcoal returned a date range of 191 cal. BC to cal. AD 2, placing the building firmly in the Iron Age, and suggesting the site was occupied for some time before the rath that now contains its footprint was ever built. Two further houses of a similar circular form were identified immediately to the south, indicating that what stood here was not a solitary dwelling but something closer to a small settlement cluster, all of it now lying beneath or beside a road that was built, in part, because the excavation had already happened.