It is only when you begin to read the edges, the low bank, the remnant ditch, the flattened oval of grass, that the human intention behind it becomes clear. This is a rath, the Irish term for a ringfort, the kind of enclosed farmstead that was built across Ireland during the early medieval period, roughly between the fifth and twelfth centuries, and which survives in the thousands, though rarely announced by anything so obvious as a signpost.

The enclosure at Ballynabinnia is oval in plan, measuring approximately 27 metres on its north-south axis and just under 24 metres east to west. Its defences, such as they are, reflect both careful construction and the particular demands of its ridge-top position. To the south and south-southeast, an earthen bank survives, modest in height but still legible, accompanied by a shallow fosse, the ditch that would once have reinforced the bank's defensive profile. A berm, the level strip of ground between a ditch and an outer bank, carries this arrangement around to the northwest. On the eastern side, the builders appear to have relied on the natural topography rather than constructing earthworks from scratch; a scarp, a near-vertical cut face rising between 1.2 and 1.8 metres, merges into the steep slope below, making the ridge itself part of the enclosure's boundary. Two ramp entrances survive, one to the south at two metres wide, one to the north-northwest at five metres, both showing signs of continuing use in more recent times. The interior is uneven, level on the western half but dropping sharply toward the east by as much as 1.5 metres, a consequence of the ridge's own irregular profile beneath the built-up ground.