It is not a ring fort, not an ancient burial monument, but a tree-ring, the surviving ditch that once defined a formal circular tree plantation, the kind of ornamental landscape feature fashionable among the owners of large Irish estates in the eighteenth and nineteenth centuries.

Before the houses came, this ground formed part of the old St Helen's estate, an area of open pasture that sloped gently from south to north towards Dublin Bay, roughly 1,100 metres to the north. The site sits between the 34 and 35.5 metre contours, a modest but perceptible rise in the land. The circular feature was first picked out in aerial photography through a CUCAP image, reference AVS 261, which drew enough attention for testing to be carried out in 1990. That investigation, recorded by A. Halpin in 1991, confirmed what the cropmark suggested: a ditch enclosing a diameter of approximately 51.5 metres externally, 2.2 metres wide and 1.7 metres deep, varying in cross-section between a U-shape and a truncated V-shape. These proportions are consistent with the kind of ornamental planting enclosure that estate landscapers used to define a ring of trees, often beech or other hardwoods, forming a visual accent in the designed landscape of a country house demesne.

The site today sits within the green space of the housing development, which means it is accessible without any particular effort. There is nothing dramatic to see at ground level, and that is rather the point. What visitors are looking at, if they know to look, is the ghost of a designed landscape, a ditch that once kept grazing animals away from a ring of planted trees on a gently sloping Dublin estate. The aerial photograph that first identified it remains the most legible view; at ground level, an awareness of the slight change in topography and the outline of the green space is probably the most a visitor can expect.