Known in Irish as cillíní, singular cillín, these were informal plots used for the interment of unbaptised infants, and occasionally others considered outside the bounds of formal Catholic burial, including stillborn children, suicides, and strangers. The one recorded near Mountpleasant in County Mayo is one of hundreds of such sites catalogued across the island, each one a quiet reminder of how religious doctrine once shaped even the most private of griefs.

The theology behind cillíní was straightforward and, by later standards, severe. Catholic teaching held that unbaptised souls could not enter heaven, and so the bodies of such children were barred from consecrated ground. Families, unwilling to see their infants buried without any ceremony or marker, instead used marginal spaces, old ringfort banks, boundaries between townlands, coastal edges, or plots already associated with early Christian use. The choice of location was rarely random. Many cillíní cluster around the ruins of early medieval churches or enclosures, places that carried a sense of sanctity even without official Church sanction. The Mountpleasant site in Mayo fits within this broader pattern, located in a county where such grounds are relatively numerous and where the practice persisted well into the twentieth century in some communities.