That quiet overwriting of an ancient boundary is, in its own way, more telling than anything deliberately destroyed.

A rath, as ringforts of this earthen type are commonly called, was typically a farmstead enclosure of the early medieval period, roughly the fifth to twelfth centuries, used to protect a family, their livestock, and their status. The Birrinagh example sits on an east-south-east-facing slope in pasture, its raised circular platform measuring 36.1 metres in diameter. The enclosing bank of earth and stone is still reasonably substantial, between 5.7 metres wide and up to 0.8 metres high in places, and the external fosse, where it survives, reaches 1.55 metres in depth and retains some waterlogging. The laneway has claimed the fosse along the north-north-east to east arc, while infilling has obscured it further around the south and south-west. A report from 1990 suggested the original entrance was probably at the south-east, a section now buried under dense scrub growth. The interior itself is not flat; it slopes noticeably from west-north-west down toward the east-south-east, which may reflect how the ground was originally shaped to aid drainage within the enclosed space.