On the north-eastern slope of Knockaulin, an enclosure exists that no one walking the ground would ever notice. There is nothing to see there, no earthwork, no raised rim, no dip in the grass. The only evidence of it comes from a single aerial photograph taken in 1967, in which the buried outline of a fosse, a defensive or boundary ditch, shows up as a cropmark, the faint differential in how plants grow over disturbed or compacted soil betraying what lies beneath. From that image, archaeologists were able to estimate a roughly circular enclosed area of around thirty metres in diameter, with what appears to be an entrance gap on the western side.

Knockaulin itself, known in Irish as Knockaillinne, is no ordinary hill. It was one of the great ceremonial sites of early Ireland, associated with the kings of Leinster and with the pre-Christian festival of Imbolc. The enclosure on its north-eastern terrace sits in what is now mixed pasture and tillage, a working agricultural landscape that has quietly buried whatever structures once stood inside that ditch. A second, smaller cropmark site lies approximately eighty-five metres to the north-west, suggesting this part of the hillside may have held more than one feature of significance, though the relationship between the two, and what either of them was actually used for, remains unknown.