That is, almost literally, nothing: no mound, no earthwork, no stone, no marker of any kind in the rough wet pasture at Tankardstown in County Limerick. And yet beneath or within that unremarkable field there almost certainly lies a prehistoric barrow, a burial mound enclosed by a circular ditch, detectable only as a faint shadow in the grass when conditions are just right and a camera is directly overhead.

The site came to light not through excavation or fieldwork but through the unlikely intervention of a gas pipeline. In November 1984, aerial photographs were taken at a scale of 1:5000 during the Bórd Gáis Éireann Curraleigh West-Limerick pipeline survey, and examination of those images revealed a small circular cropmark, the telltale signature of a buried ditch. Cropmarks appear when differential moisture or soil conditions, caused by a buried feature below, affect plant growth above, so that from the air a ring of slightly different vegetation betrays what lies beneath. The site was catalogued as possible site number 040244. It sits in the western quadrant of a wider cluster of barrows recorded in the same area, suggesting this corner of Limerick was once a significant funerary landscape. It does not appear on any Ordnance Survey historic maps, and orthophotography taken between 2005 and 2012 showed no surface trace whatsoever. A faint circular cropmark was again just barely visible on Google Earth imagery from April 2013 and March 2016, confirming the buried feature persists, even if the land above gives nothing away. The record was compiled by Fiona Rooney and uploaded to the national monuments database in May 2021.

For anyone curious enough to seek it out, the practical reality is that there is no monument to stand beside and no interpretive panel to read. The field is rough and wet, and access would require appropriate permissions from the landowner. What makes a visit worthwhile, if it can be called that, is the exercise in imagination it demands: standing on ordinary farmland in County Limerick, knowing that the only people to have documented what lies below did so from thousands of feet in the air, on a November day in 1984, while photographing a gas route.