Beneath and behind it, folded into its fabric, are the remains of a far older boundary: an early medieval ecclesiastical enclosure whose earthen bank and surrounding fosse, a defensive ditch, predate the stone wall by centuries. The enclosure is roughly circular, about 63 metres across overall, and it follows a pattern common to early Irish monastic and church sites, where a circular earthen rampart defined sacred space and separated the spiritual interior from the secular world outside. What makes Rathcusack quietly unusual is how legibly this older geometry survives, half-absorbed into later construction rather than erased by it.

The sequence of building here tells its own story. The original enclosure consisted of an earthen bank, still standing to an internal height of around 1.1 metres and an external height of 1.7 metres, with a width of roughly 7 metres, set just outside a fosse approximately 3.7 metres wide and 0.6 metres deep. At some later point, a stone wall was raised to enclose a graveyard, and rather than clearing the earlier earthworks, the builders set this wall directly on top of the fosse, incorporating the internal bank into the new structure. A medieval church sits centrally within the enclosure, as was typical, the sacred building placed at the heart of the bounded space it shared with the community it served. The site occupies a gentle west-facing slope with open views to the south, west, and north, and the River Nore runs roughly 300 metres to the west.

The earthen fosse is most clearly visible where it projects beyond the line of the stone wall in the southern sector, from roughly east-south-east around through south to south-south-west. On the western and north-western sides it has been infilled and is no longer easy to read. For anyone with an eye for earthworks, the southern arc is where the original enclosure announces itself most plainly, a low curve in the ground that connects this quiet Kilkenny churchyard to a much earlier way of organising the sacred landscape.