The enclosure measures about 46.5 metres east to west and 38 metres north to south, its earthen bank rising to a maximum height of two metres and ringed on the northern and southern sides by an external fosse, or ditch, still a metre deep. Three gaps interrupt the bank, the widest of them on the west-northwest side at four metres across, the others to the east and south-southeast. A silage shed now stands just outside the bank to the northeast, the most visible sign that this is a working agricultural landscape as much as an archaeological one.

This is a rath, the most common monument type in the Irish countryside. Raths are ringforts built during the early medieval period, roughly between the fifth and twelfth centuries, and typically served as enclosed farmsteads for a single family or small community. The earthen bank and ditch were less about military defence and more about defining a household boundary, keeping livestock in and wolves out. What makes this particular example worth a second look is a possible souterrain in the northern half of the interior. Souterrains are underground stone-built passages or chambers, often associated with ringforts and thought to have been used for storage, refuge, or both. Whether the one at Ballymurphy is intact or partially collapsed is not certain, but its potential presence adds a subterranean dimension to what might otherwise seem a straightforward earthwork.