That gentle arc is not merely a quirk of construction; it may be the surviving outline of an early ecclesiastical enclosure, the kind of roughly circular boundary that once demarcated sacred ground in early medieval Ireland, separating a monastic or church settlement from the surrounding landscape.

The observation was made by researcher Swan in 1988, who noted that the circular form of the graveyard's boundary wall pointed to the possible presence of such an enclosure. Early ecclesiastical enclosures of this type are generally understood to predate the formal parish system, and their circular or subcircular plan reflects an older tradition of defining sacred space. They are often the earliest physical evidence we have for Christian activity in a given locality, the church or monastery itself having long since vanished, leaving only the shape of its boundary fossilised in a later wall or field boundary. In this case, the graveyard wall at Castletown appears to preserve just such a memory in its curve.