On the flat, open grassland of the Curragh in County Kildare, a shallow U-shaped earthwork sits quietly in the turf, most legible not from ground level but from the air. Picked up in a Department of Defence aerial photograph from 1999, the feature measures roughly five metres along its northwest to southeast axis and just under four metres wide, open at its southeastern end. A fosse, meaning a shallow ditch dug into the ground, defines its outline, running no deeper than about forty centimetres at its most pronounced. A pair of small, parallel, sub-rectangular depressions lies a further three metres to the southeast, aligned with the open arms of the U, suggesting the whole arrangement is a single structure rather than a coincidence of separate features.

What the earthwork actually represents is uncertain. The Curragh has been associated with military training and manoeuvre for centuries, and the leading interpretation is that this feature may be a product of that long martial use of the plain. The form does not obviously match the typical profile of a prehistoric enclosure or a medieval earthwork, and the shallow, almost tentative nature of the fosse, combined with the curious rectangular depressions, leaves open the possibility of some kind of field fortification, gun emplacement, or training earthwork from a more recent period. Without excavation, the question stays open.