It is probably the footprint of a house, though the word "probably" carries some weight here. Nobody has been able to say with confidence when it was built, who lived inside it, or precisely how it was used.

A cashel is a type of early Irish stone enclosure, essentially a roughly circular walled fort or farmstead, typically associated with the early medieval period though some examples are older or later. The structure at Ballybranagan sits within one such enclosure. The circular house form itself is an ancient one in Ireland, found across prehistoric and early historic contexts, and a diameter of around 5.8 metres would have provided a modest but workable living space. The defining feature here is the line of upright slabs rather than coursed walling, which may reflect either the original construction method or simply what has survived over time. Without excavation, the relationship between the house site and the cashel wall that surrounds it remains an open question.