A ringfort, or rath, is an enclosed circular or oval settlement of the early medieval period, typically defined by one or more earthen banks and ditches. This one was originally bivallate, meaning it had two such banks, making it a more substantial and likely more prestigious enclosure than the simpler single-banked examples scattered across the Irish countryside. What makes it quietly peculiar is its location: not on high ground commanding a wide view, as many ringforts favour, but on low, wet ground at the river's edge, where the estuary and the marsh have been doing their slow work of reclamation.

A surveyor named McCaffrey recorded the fort in detail, describing an inner bank reaching an external height of around 3.1 metres, separated from an outer bank by a fosse, or ditch, nearly 5.7 metres wide. The interior measured roughly 56 metres north to south and 37 metres east to west, dimensions that suggest a reasonably large enclosure. By the time of a field inspection in December 1982, however, the picture was considerably reduced. Only the inner bank remained clearly traceable, and even that had diminished substantially, standing just 0.35 metres on the interior at its eastern side. To the north, east, and south, the bank had eroded to the very lip of the river. Along the southern and western arcs it was so badly defaced as to be nearly invisible. The double-banked fort that McCaffrey had described had, in the intervening years, become something closer to a ghost of an earthwork, legible only in fragments.