What makes it worth a second look is not dramatic height or elaborate construction, but the particular way it has been absorbed into the working landscape, the southern field bank doubling as the boundary line between Cloonsillagh and the neighbouring townland of Crotta, old land divisions and ancient enclosure folding into one another across the same strip of earth.

The site is a univallate rath, meaning it has a single enclosing bank rather than the multiple concentric rings found at more elaborate examples. A rath of this kind would typically have served as a farmstead enclosure during the early medieval period, roughly the fifth to twelfth centuries, protecting livestock and a family's domestic space within a raised earthen ring. At Cloonsillagh, that bank is still well defined, running to about six metres wide at its base and reaching 1.4 metres above the exterior ground level, though only 0.6 metres above the interior, which gives a sense of how the ground level inside the enclosure sits slightly raised. The enclosed area is sub-circular rather than a perfect ring, measuring around 20 metres across one axis and 29 metres across the other. An exterior fosse, the shallow ditch dug outside the bank when the earth was thrown inward, survives on the northern through to the southern arc, where it is still roughly four metres wide. Elsewhere, the construction of later field banks has made it impossible to trace.