That ambiguity is part of what makes the site worth knowing about.

What the aerial observations recorded was a double wall or bank and fosse, the fosse being a defensive ditch typically dug in front of an earthen rampart, cutting off an area south of a natural swallow hole, a point where surface water disappears underground through a gap in the rock. A short distance to the north, a second headland showed a depression running across its narrow isthmus. Together, these features are consistent with a promontory fort, a type of coastal enclosure in which builders used a headland's natural edges as most of the defensive perimeter, adding artificial banks and ditches only where the land connected to the mainland. They are found throughout Ireland's Atlantic coastline and range in date from the Iron Age through to the early medieval period. Whether the Killelan features represent a genuine fort of this kind remains unverified; Casey's 2003 assessment is careful to describe it only as a possibility, noting that the terrain, mountainous bog and outcropping rock, made ground investigation impractical. The site is also overlooked by higher ground to the east, which would have been a significant tactical disadvantage for any defended enclosure and adds a further layer of uncertainty to the interpretation.

The combination of a swallow hole, a second candidate headland nearby, and earthworks visible only from altitude gives the place a quietly layered quality, even if the archaeology beneath the bog remains unresolved.