It is invisible at ground level, revealed only from the air, where the buried outline of a semi-circular structure roughly 48 metres in diameter shows up as a cropmark, the kind of faint but legible trace that warm, dry summers occasionally press into the surface of ploughed and planted ground.

Cropmarks form when buried features, walls, ditches, or banks, affect the moisture content of the soil above them. In dry conditions, crops growing over a buried ditch tend to stay greener longer, drawing on residual moisture, while those above a compacted surface or buried wall show stress earlier. Seen from height, these differences in colour and growth register as ghostly outlines of structures that may have vanished from the surface entirely. The Rathronshin earthwork came to attention through a Google Earth orthoimage captured on 19 July 2021, when conditions were evidently right for the underlying archaeology to make itself known. The semi-circular form, at around 48 metres across, is substantial enough to suggest something significant once stood or was enclosed here, though without excavation the precise nature and date of the feature remain open questions.

The site sits in ordinary agricultural land, next to a small quarry, and there is nothing on the surface to mark it out. Its existence, for now, is a matter of archive and aerial image rather than anything a visitor could observe on foot.