That uncertainty is part of what makes it interesting. The site sits low and south-facing, cut off from the surrounding land by a deep fosse and an earthen bank, the classic arrangement of a promontory fort, where a headland is defended on its landward side by one or more earthen or stone barriers, leaving the sea itself to guard the remaining perimeter. A second bank once reinforced that boundary, but erosion has reduced it to traces. What little interior the site ever had has been almost entirely lost, leaving something that could be read as a defensive enclosure or simply as a trick of the landscape.

The ambiguity was noted by Casey in 2003, whose survey recorded the site as a possible promontory fort while acknowledging that the remains were insufficient to confirm its origins with any confidence. Promontory forts are found all along the Irish Atlantic coast and are generally associated with the Iron Age, though some were used across many centuries. At Killelan, the surrounding land offers a small contextual clue: the area around the promontory is fertile, cleared pasture, with traces of earlier cultivation visible beneath the present fields. That layering of land use is common in coastal Kerry, where generations of farming have reworked the same ground, sometimes obscuring and sometimes accidentally preserving earlier features. Whether the fosse at Killelan was dug to protect people, livestock, or something else entirely remains an open question.