This is a rath, the most common type of early medieval enclosure in Ireland, typically consisting of one or more circular earthen banks with a ditch, known as a fosse, dug between them. Most were farmsteads, home to a single family and their livestock, and they were built in their thousands across the Irish landscape between roughly the fifth and twelfth centuries. The one at Ballycahill is bipartite, meaning it has two banks with a fosse running between them, which places it slightly above the most basic single-bank examples in terms of effort and perhaps social standing.

The enclosure measures approximately 64 metres east to west and 57 metres north to south, making it a reasonably substantial example. Its preservation is uneven. The inner bank is the most legible portion, tracing an arc from the north-west around through the east and down to the south-south-west. Elsewhere, the original bank has been reduced to a simple scarp, a sloping edge in the ground where the earthwork has worn away or been disturbed. The fosse can be followed from the north, around the eastern side, to the south-east, while the outer bank remains visible along the western and northern stretches. Reading the site requires a degree of patience and a willingness to walk the full circuit, piecing together surviving sections with flattened or eroded gaps in between.