The enclosure measures around 26 metres in diameter, its irregular outline still legible from aerial photography, tracing the remains of a cashel, the term used for a stone-walled ringfort of the kind built across Ireland, particularly in the west, during the early medieval period.

A cashel differs from the more familiar earthen ringfort in that its boundary is formed from dry-stone walling rather than banked soil and ditch, a distinction that reflects both the local geology and the building traditions of communities who had limestone and sandstone close to hand. The Aillwee example occupies a plateau at the hill's summit and sits within a broader field system that appears to belong to more than one historical phase, suggesting that people were organising and working this landscape across a considerable stretch of time, not just during the period when the cashel itself was in use. The enclosure has been identified through Ordnance Survey ortho photography taken between 2013 and 2018, as well as through Digital Globe imagery, meaning its form survives well enough to read from above even if its walls have settled and spread over the centuries.