What exists here is a ring-ditch, roughly ten metres in diameter, that is invisible at ground level and only became legible from the air, showing up as a cropmark on an aerial photograph taken on 20 August 1991. Cropmarks of this kind appear when buried features, such as the filled-in ditches that once surrounded prehistoric burial mounds or ritual enclosures, affect the growth of crops above them, producing differences in colour and height that can be read from altitude even when the landscape below looks entirely ordinary.

What makes the Threecastles example particularly interesting is that it does not stand alone. The same 1991 aerial photograph captured three further ring-ditches lying to the south-east, at distances of roughly 140m, 190m, and 240m from this one. The four together suggest a concentration of prehistoric funerary or ceremonial activity across this stretch of Kilkenny tillage land, a cluster that would be entirely undetectable on the ground. Since that photograph was taken, the R693 road has been constructed running north-west to south-east through the area, cutting between the monuments and dividing the group, with two ring-ditches now lying to the east of the road and two to the west. The road itself has left the buried archaeology undisturbed in the sense that the cropmarks remain, but the landscape these features once shared has been divided in a way that makes their relationship harder to read from the ground.