That combination of engineered bank and living watercourse is not accidental. The result is a monument that has, in effect, been moated on one side by human effort and on another by the landscape itself, the south-western section of the external fosse, a defensive ditch dug to accompany the earthen bank, remaining water-filled to this day.

The enclosure measures roughly 35 metres east to west and 32 metres north to south, making it a modest but coherent space, and it survives in notably good condition. A gap of around four and a half metres on the eastern side may be the original entrance, which would have faced away from the wettest, most defensible arc of the perimeter. Inside, in the south-western portion of the interior, two raised subrectangular platforms survive: a smaller one to the west, roughly four metres by three and a half, and a larger one to its east, approximately six metres by five and a half. Platforms of this kind within enclosed sites are often interpreted as the footprints of vanished structures, whether domestic buildings, storage facilities, or something less easily categorised. No date has been firmly established for this particular enclosure, and the marshy setting makes it difficult to assign confidently to any single period or tradition. Earthwork enclosures of broadly similar character appear across Ireland from the early medieval period onward, though the particular interplay here between the stream, the fosse, and the raised interior areas gives Corlackan its own quiet logic.