What makes it quietly significant is its context: it is the third of three conjoined cells, a cluster of adjoining stone rooms built one against the other within the sheltered interior of the fort. Promontory forts use a headland's natural clifftops and steep drops as their primary defence, with a wall or bank cutting off the landward side, and whoever lived or sheltered here would have had the sea on most sides.

The antiquarian Thomas Johnson Westropp recorded the three cells together in 1911, describing walls between three and four feet thick and this particular example as a circular annexe measuring fifteen feet across internally. The substantial wall thickness relative to the modest interior diameter suggests a structure built to last, though its date remains unknown. Westropp's description captured it at a moment when more of the fabric still stood; since then, only fragmentary traces have remained, the two companion cells nearby in a similarly reduced state.