This is a rath, the Irish term for a ringfort, the most common monument type in the Irish landscape. Thousands were built, mostly during the early medieval period, and they functioned primarily as enclosed farmsteads, their banks and ditches marking out a household's space rather than defending against any serious military threat. What makes the Cullomane example quietly interesting is the combination of features still legible in the ground.

The enclosure measures roughly 26.8 metres north to south and 37.8 metres east to west, giving it a slightly elongated oval plan. The bank running from the west around to the south-east is earthen and partly stone-faced, suggesting some deliberate construction effort beyond a simple thrown-up mound. From the south-east back around to the west, the boundary changes character, becoming a scarp, essentially a cut or shaped slope in the natural ground, with a slight internal lip still visible. Outside the bank, a fosse, the ditch that would originally have been dug to provide the material for the bank itself, is now silted up and largely filled in. The entrance, a break in the bank on the eastern side measuring about 5.2 metres wide, has been blocked at some point with stones, which may reflect later agricultural reuse of the site rather than any original design. Running across the interior, east to west, are cultivation ridges, the low parallel earthworks left by ridge-and-furrow farming, a system widely used in Ireland from the medieval period onwards and still visible on old pasture that has escaped the plough. Their presence inside the ringfort suggests the enclosure was turned over to tillage at some stage after it ceased to function as a settlement.