This is a rath, the most common type of early medieval enclosure in Ireland, typically built between roughly 500 and 1000 AD as a farmstead surrounded by earthen banks designed to protect livestock and household. What makes the Knockaninane example worth attention is the relative completeness of its double-ring plan, a feature that would originally have signalled a degree of status or wealth above that of the single-banked majority.

The site measures 32 metres across in both directions, defined by two concentric banks separated by a fosse, the term for the ditch dug to provide the material that formed the banks themselves. The inner bank is the more substantial of the two, reaching an external height of 2 metres and a width of 6.4 metres, though it has been breached in numerous places, partly by cattle and partly by the natural slumping of material into the intervening fosse. The outer bank, 2.7 metres wide and 1.7 metres high externally, carries a break at its northern arc and shows what appears to be recent stone-facing along its eastern side. A possible causeway entrance, roughly 2.5 metres wide, survives at the north-west. The convex interior, which rises slightly toward the centre as is common in raths of this kind, contains two further features of interest: a possible souterrain and a possible hut site, both in the southern half. Souterrains are underground stone-lined passages associated with early medieval settlements, likely used for storage or refuge. A depression just outside the outer bank at the north-west, approximately 5 metres long and 2 metres deep, is the result of quarrying rather than any original feature of the enclosure. A farm lane constructed in the late 1990s now skirts the outer bank from the north-east around to the south, and the ground level was lowered to accommodate it, altering the immediate setting on that side.