This one, in reclaimed pasture at Tankardstown in County Limerick, is barely there at all. It exists, for now, primarily as a small circular cropmark, the kind of faint impression that only becomes legible from the air, and even then only under the right conditions. Whether it is genuinely prehistoric or simply a trick of the ground is, officially, still an open question.

The site came to attention not through archaeological survey in the traditional sense, but through an unlikely intermediary: a gas pipeline. Aerial photographs taken on 3 November 1984 for Bord Gáis Éireann, as part of their pipeline documentation work, captured what appeared to be a circular cropmark in the field below. Cropmarks of this kind form when buried features, such as a filled ditch surrounding a burial mound, affect soil moisture in ways that alter how overlying grass or crops grow, producing outlines that are invisible at ground level but readable from altitude. The mark reappeared in Ordnance Survey orthophotography taken between 2005 and 2012, and again in Google Earth imagery, suggesting that whatever is producing it is consistent and not simply an artefact of a single photographic moment. The site sits in the eastern quadrant of a wider cluster of barrows, a barrow being a mounded earthwork raised over a burial, with a surrounding ditch, and is catalogued alongside several neighbouring monuments. It was compiled by Fiona Rooney and uploaded to the national record in May 2021. Notably, it does not appear on any of the Ordnance Survey's historic maps, which is itself a small puzzle.

There is an honest caveat attached to this site: those who recorded it flag it as having doubtful antiquity, noting that the wet ground visible around the earthwork could indicate a natural hollow or pond feature rather than anything man-made. Visiting would mean walking reclaimed farmland, and there is nothing to see at ground level that would distinguish this from any other damp corner of a field. Its interest lies almost entirely in the forensic process by which it was identified, and in the uncertainty that still surrounds it, a monument that may not be a monument at all, still waiting for a definitive answer.