When it was first entered into the Sites and Monuments Record in 1986, it was catalogued as an enclosure, a term that usually implies something ancient, a defended settlement, a ritual boundary, a feature shaped by early medieval or prehistoric hands. The cartographic evidence that prompted the listing told only part of the story.

What the feature actually turns out to be is a piece of deliberate landscape design. The oval, measuring roughly 80 metres along its north-south axis and 60 metres east to west, is surrounded by a water-filled fosse, essentially a moat-like channel approximately 7 metres wide. The combination of scale, geometry, and the managed water feature points not to an ancient enclosure but to the ornamental landscaping tradition that accompanied great Georgian estates. Russborough House itself is one of the more celebrated examples of Palladian architecture in Ireland, and demesnes of this kind were frequently laid out with carefully contrived earthworks, water features, and planted enclosures designed to create atmosphere and prospect rather than defence or agriculture. This particular feature, island-like within its filled channel, fits comfortably into that tradition, even if its precise original purpose within the wider designed landscape is not documented in the available record.