On the northern bank of the Kilcolgan River in County Galway, a D-shaped earthwork roughly 42.5 metres across occupies the edge of a steep cliff-like slope, and nobody is entirely sure whether that flat side of the D was planned or simply eroded away over time. It is the kind of ambiguity that tends to get smoothed over in casual accounts of ancient monuments, but here it sits at the centre of what the place actually is.

Raths, also called ring-forts, were enclosed farmsteads of the early medieval period, typically circular in plan and defined by one or more earthen banks with a ditch, known as a fosse, dug between them. Rahaneena Fort follows that general pattern, with two banks and an intervening fosse, though the outer bank has been largely demolished by a laneway that cuts around the monument from west through north to east. Scholars including Redington in 1912 and Westropp in 1919 noted the site, and McCaffrey recorded it in more detail in 1952, by which point its condition was already compromised. The fosse, which would once have served as a drainage and defensive feature, is currently used as a rubbish dump. Dense overgrowth further obscures whatever remains of the enclosing earthworks.

The cumulative effect of laneway construction, dumping, and vegetation is that very little of the monument is now legible from the ground. The cliff-edge position on the Kilcolgan River presumably made the site attractive in the first place, offering natural defence on one side. Whether the D-shape is a deliberate feature, taking advantage of that topography, or simply the consequence of centuries of erosion at the scarp edge, is a question that current vegetation and disturbance make difficult to resolve without more systematic investigation.