The structure is roughly thirty metres across, and what survives of it traces the logic of an enclosure that once meant something to the people who built it, though time and the accumulation of field clearance have done their slow work of erasure.

This is a ringfort, or at least what the archaeological record classifies as a circular enclosure of that type. Ringforts were the dominant form of rural settlement in early medieval Ireland, typically dating from around the sixth to the twelfth century, and thousands of them survive across the country in varying states of preservation. They were enclosed farmsteads, the bank and fosse (a fosse being a defensive ditch dug around the outer edge of the bank) providing both a physical barrier and a social signal of status. At Annagh, the fosse is clearest along the northern and eastern arc, where it retains something of its original depth and shape. Elsewhere, rubble from field clearance has gradually filled it in, a common fate for earthworks in agricultural land where stone is routinely gathered and dumped wherever a hollow presents itself. Fragments of stone revetment, the facing material used to stabilise and reinforce the inner or outer surface of the bank, are still intermittently visible along its edge, suggesting the structure was once more substantial than it now appears.