This is a rath, the Irish term for a ringfort, a type of enclosed farmstead typically built during the early medieval period, roughly between the fifth and twelfth centuries. Thousands of them survive across Ireland, but what makes this one at Ballynacor worth pausing over is the detail of its construction: not one enclosing bank but two, separated by a fosse, which is a dug ditch, with a further outer fosse beyond that. A site with this level of defensive elaboration is classified as a bivallate ringfort, and the additional effort involved in throwing up two banks and cutting two ditches suggests that whoever lived here either had something worth protecting or the social standing to command that kind of labour.

The monument measures roughly forty metres across at its widest, and the interior slopes gently from north to south, following the natural incline of the hillside. The inner bank remains well preserved. The outer bank is more intermittent, clearest on the north-west to north-east arc and again from the south-east to south-west, with only a slight trace of the outermost fosse visible on the northern side. At the south-east, there is what appears to be an entrance gap about one and a half metres wide, a narrow threshold that would have controlled access into the interior. The elevated position on the hill gives long sightlines across the surrounding landscape, a characteristic shared by many ringforts whose builders clearly valued visibility as much as enclosure.