Nobody recorded what it was for, and it no longer exists. What remains is a reference in a 1931 publication and the faint implication of something deliberate having been built and then lost entirely to the landscape.

O'Sullivan, writing in 1931, noted the structure's position about a hundred metres to the south-east of Cahernagat, itself a ringfort, which is the term for a roughly circular enclosure, usually defined by earthen banks or stone walls, that served as a defended farmstead in early medieval Ireland. Whether the structure on Croaghmarhin was related to Cahernagat, served a similar residential or agricultural purpose, or was something else entirely, was never established. Its modest diameter and circular form might suggest a small outbuilding, a pen, or a shelter of some kind, but the archaeology does not support a firm conclusion. By the time the Dingle Peninsula was formally surveyed for the Corca Dhuibhne Archaeological Survey, compiled by J. Cuppage and published in 1986, the feature had already vanished from the ground entirely.