On the wooded shoulder of Mountseskin Hill on the southern edge of the Dublin mountains, a prehistoric cairn, that is, a mound built from piled stones and earth, sits recorded on the national monuments register under the reference DU024-024. It is roughly eight metres in diameter. It is not especially large, and it is not especially easy to locate. That, as it turns out, has been rather the point.

The cairn was one of a group on Tallaght Hill and appeared on the first edition Ordnance Survey six-inch map of 1837 as a circular mound sitting atop an elongated ridge to the west of Knockannavea. By the time the revised OS twenty-five-inch map was produced in 1863, the site had disappeared from the survey altogether, suggesting it had already been significantly disturbed or reduced. When archaeologists inspected it in 1994, a new forest track had been driven directly through the middle of it. A further inspection in 2013 identified what appeared to be the monument in a rectangular clearing to the east of that track, and this location became the subject of a formal archaeological assessment in 2016, carried out over four days in February of that year by archaeologist Edmond O'Donovan under licence number 15E0509. The results were deflating in one sense and clarifying in another: the mound in the clearing was modern, of no archaeological significance, and the real cairn was found to lie approximately ten metres to the northeast, on an area of forest track on land undisturbed since afforestation in around 1993. That surviving remnant, sitting where the ground drops away on all four sides, corresponds both with the position marked on the 1837 map and with the physical description recorded during the 1994 survey.

The site lies within commercial woodland, which means access is limited and the terrain is not straightforward. The forest track that bisects the original monument is a reminder of how casually infrastructure can cut through a recorded site, and the sequence of misidentification across 2013 and 2016 is itself an instructive piece of recent archaeological history. Anyone with a serious interest in the area would do well to consult O'Donovan's 2017 report before visiting, and to note that the actual surviving mound is not the clearing that might first draw the eye, but a lower, less obvious feature to its northeast, partially obscured by the trees planted during afforestation three decades ago.