The structure at Lisnagry is a rath, the most common type of early medieval enclosure in Ireland, typically formed by throwing up a bank of earth around a domestic or farming space and digging a fosse, or ditch, along the outer edge. What makes this example worth pausing over is how well it has survived: the bank remains clearly defined, and the external fosse is still visible around much of the circuit, running from the south, around through the west, and up to the north-northwest.

Raths were built across Ireland roughly between the fifth and twelfth centuries and served primarily as farmsteads, the bank and fosse offering a modest but meaningful boundary against livestock straying and neighbours encroaching. This one measures approximately 31 metres in diameter, a fairly typical scale for a single-family enclosure of the period. What distinguishes the interior of the Lisnagry example from many comparable sites is a natural east-west ridge running through it. Whether that feature influenced where the rath was sited in the first place, or simply happened to fall within the chosen boundary, is not recorded, but it gives the interior a subtle topographic character that a flat site would lack. The surrounding pasture, now unremarkable to look at, would once have formed part of the working land attached to whatever household sheltered here.