This is the fort at Lisavargy, a roughly circular enclosure measuring 54 metres across in both directions, and it belongs to a category of monument that once dotted the Irish countryside in the thousands.

The site sits towards the southern end of a NNW-SSE drumlin ridge, just off the summit, with its interior sloping down to the east. A drumlin is a smoothed, elongated hill formed by retreating glaciers, and in counties like Monaghan they cluster so densely that the landscape becomes a kind of rolling basket-weave of ridges and hollows. Whoever chose this particular spur was almost certainly thinking about visibility and defensibility. The enclosure is defined on its eastern and southern sides by a scarp, roughly a metre high and just under two metres wide, backed by an outer fosse, that is, a ditch, with a base width of about 2.8 metres. Elsewhere, the boundary has been quietly swallowed by the agricultural landscape around it. There are two gaps in the perimeter, one to the east-northeast and one to the west, but both appear to be modern breaks rather than the original entrance, which has not been identified. In that small uncertainty lies something quietly suggestive: the people who last used this place regularly knew exactly where they were going in, and we do not.