The site at Curraghnalaght is a rath, a type of ringfort that served as a defended homestead, typically constructed during the early medieval period in Ireland. This one is roughly circular, measuring 27.4 metres in diameter, and its bank retains an unusual detail: the inner face is stone-lined, giving it a more substantial finish than the simpler earthen raths found elsewhere.

The most quietly remarkable aspect of this site came to light not through excavation but through agriculture. In 1936, corn was planted across the interior of the rath and in the surrounding field. When it grew, it did not grow evenly. Researcher Hartnett, writing in 1939, recorded that the differential growth patterns visible in the crop revealed the buried outline of a fosse, the defensive ditch that would originally have ringed the bank, and possibly a second outer bank beyond it. Cropmarks of this kind occur because disturbed or filled soil retains moisture differently from undisturbed ground, causing plants rooted in it to grow at a different rate or colour. What was invisible at ground level became legible from above, traced in the uneven height and vigour of a field of corn.