These sites, known in Irish as cillíní (the singular is cillín), were the designated resting places for unbaptised infants, and sometimes for others considered outside the boundaries of consecrated ground, including stillborn children, people who died by suicide, and strangers whose origins were unknown. The Catholic Church's doctrine of limbo, which held that unbaptised souls could not enter heaven, meant that official parish cemeteries were closed to these children for centuries. Their families buried them instead in places already understood to carry a certain liminal sanctity: old ring-forts, early medieval ecclesiastical enclosures, coastal strands, and boundary ditches. A cillín was not a place of disgrace so much as a place apart, and the grief surrounding it was largely private and unrecorded.

Thousands of these sites survive across Ireland, many of them unmarked or identified only through local memory and oral tradition. They cluster most densely in the west of the country, where the old Gaelic and early Christian landscape has been less thoroughly disrupted. Clare has a considerable number, tucked into field corners and overgrown enclosures, often identifiable by low, irregular mounding or by the presence of small uninscribed stones. The Knock site belongs to this broader pattern, a fragment of a practice that continued in parts of rural Ireland well into the twentieth century, long after official theology had begun to soften on the question of infant salvation.