These grounds, known in Irish as cillíní (singular cillín), served for centuries as the burial places of unbaptised infants, and occasionally of others considered to exist outside the formal rites of the Catholic Church, including stillborn babies, those who died by suicide, and strangers whose origins were unknown. They occupy a quietly distinct position in the Irish landscape, neither fully sacred nor fully secular, usually located at townland boundaries, beside old ringforts, or at the edges of ancient ecclesiastical sites.

The cillín tradition reflects a particular and now largely abandoned theological position, in which unbaptised children were believed to be excluded from consecrated ground. Families who could not bury a child in the parish churchyard would instead carry the small body, often at night and with little ceremony, to one of these marginal places. The sites were chosen with care, frequently near locations already understood to carry spiritual weight, old ruins, holy wells, or the earthworks of earlier settlements. The grief attached to these places was real, and their continued presence in the landscape is a reminder of how recently that practice persisted; in some parts of rural Ireland, cillíní were in use well into the twentieth century.