At Ballynakill in County Tipperary, a bivallate ringfort, meaning one enclosed by two concentric banks rather than the more common single ring, sits at the northern end of a natural ridge. The hillock it occupies was not simply built upon but worked into: the edge of the natural rise was cut away to create an internal scarp and an external counterscarp bank, so the earthworks and the topography are inseparable, each reinforcing the other.

The fort is roughly circular, measuring just under 46.5 metres north to south and 45.5 metres east to west. The inner bank, the fosse (a U-shaped ditch), and the outer bank together form the double enclosure typical of a more elaborately defended or higher-status rath, the Irish term for an earthen ringfort of early medieval date, most commonly associated with the period between roughly the sixth and tenth centuries. Bedrock lies close to the surface throughout the site, and stones and small boulders push through the outer bank in places, giving it an irregular, stony texture. That same geology accounts for some of the damage. The northern portion of the outer bank is heavily worn, and the inner edge in that area is defined by a sheer, uneven scarp of exposed bedrock, which is most likely the result of quarrying carried out at some later point. The interior has suffered similarly: the south-eastern quadrant has been quite extensively quarried. To compound the alterations, a substantial earthen field bank with a ditch on its south-western side now bisects the entire site on a north-west to south-east axis, dividing the interior in a way that would have made no sense to whoever originally built the enclosure.