What survives at Alliganstown is easy to overlook. Set at the western foot of a long, moderately steep slope, in wet and rushy pasture beside a small eastward-flowing stream, this ringfort has been worn down to something approaching invisibility. Ringforts, known in Irish as raths, were the most common form of rural settlement in early medieval Ireland, typically consisting of a circular or oval area enclosed by one or more earthen banks and ditches. Most were farmsteads, occupied between roughly the fifth and twelfth centuries. The example at Alliganstown is oval rather than circular, and retains the structural bones of a double-banked enclosure, even if those bones are now considerably eroded.

The monument measures roughly 23 metres north to south and 18 metres across internally, with the outer dimensions reaching approximately 50 by 42 metres. It was originally defined by an inner earthen bank, a flat-bottomed fosse or ditch, and a second outer bank beyond that. The fosse is about 2.1 metres wide and 0.8 metres deep where it survives. Much of the outer bank, however, has been levelled into the fosse along the south-east to north-east arc, leaving only the ENE to SE section in anything approaching its original form. The original entrance was at the ESE, where gaps in both the inner and outer banks align with a causeway across the fosse; that causeway is 4.2 metres wide and 6.1 metres long, and its preservation gives a surprisingly legible sense of how one would have approached the enclosed space. Inside the earthwork, the northern half sits about 0.6 metres higher than the southern half, a subtle internal topography that would once have been more significant for drainage and construction alike.