This is a rath, the most common type of early medieval settlement monument in Ireland, typically built between the sixth and tenth centuries as a farmstead enclosed by one or more earthen banks. The Drombeg example is univallate, meaning it has a single enclosing bank rather than two or three, and that bank, though heavily overgrown, still measures seven metres wide and rises to 1.6 metres on its outer face.

The enclosure is sub-circular, stretching roughly 35 metres north to south and 33 metres east to west, a sizeable interior by any reckoning. Outside the bank runs a fosse, a shallow defensive ditch, U-shaped in cross-section and averaging about a metre wide and somewhere between 0.4 and 0.8 metres deep. It survives best along the northern and eastern arcs; elsewhere vegetation change rather than clear earthwork is what gives the line away. Two gaps interrupt the bank, one to the south at 2.4 metres wide and another slightly larger one to the south-east at 2.8 metres, and either or both may represent original entranceways. The western sector has been absorbed into the local field system, with the bank serving as a divider between plots, a fate that has befallen many such sites across Ireland as farming patterns shifted across the centuries. Fieldbanks also press against the monument to the north-west and south-south-west, hemming it without quite erasing it.