A subcircular enclosure, measuring roughly 43 metres north to south and 40 metres east to west, sits quietly on a ridge with two earthen banks and a fosse, the drainage ditch dug between them, still legible in the ground after more than a thousand years.

This is a rath, the commonest form of early medieval settlement in Ireland, typically dating to somewhere between the sixth and twelfth centuries. Raths were farmsteads enclosed by one or more earthen banks, the interior serving as a protected space for a family and their livestock. At Ardagh, the inner bank survives well along the north-east, eastern, and southern arcs of the enclosure; elsewhere the boundary becomes a scarp, a natural or worked slope rather than a built-up bank, which still marks the line of the original perimeter. A possible entrance has been identified at the east-south-east. What complicates the picture slightly is the later field boundary that runs over the outer bank from the north-east around to the north-west, suggesting that whoever drew those agricultural lines recognised the earthwork well enough to use it as a convenient edge, even as the original purpose of the structure had long been forgotten.