Children's burial ground, An Caiseal, Co. Mayo

Known in Irish as a cillín (plural cilliní), these were informal burial places used for unbaptised infants, and sometimes for others considered ineligible for consecrated ground, including suicides, strangers, and the unbaptised poor. The Catholic Church's doctrine on limbo meant that children who died before baptism could not, under prevailing custom, be interred in a parish graveyard. Instead, families brought them to marginal spaces, often ancient earthworks, boundaries, or shorelines, places that existed somehow outside the ordinary social and spiritual order.

Cilliní are found across Ireland in their hundreds, and Mayo has a particularly high concentration of them, reflecting both the density of rural Catholic settlement and the hardships of post-Famine communities. The choice of site was rarely random. Families often selected locations already marked as old or liminal, pre-Christian enclosures, ring-forts, or the edges of townlands, places that carried their own long memory of use. An Caiseal, as a place name, suggests the presence of a cashel, a type of early medieval stone enclosure typically associated with a farmstead or ecclesiastical site, though whether the burial ground here relates directly to such a structure is not recorded. The burials themselves were generally unmarked, or marked only with a small stone, which is why so many cilliní remained unrecognised for generations, known only to local families who continued to use them quietly, sometimes into the twentieth century.

The practice of using cilliní declined sharply across Ireland during the latter half of the twentieth century as Church teaching softened and attitudes towards the burial of unbaptised children changed. In 2016, the Catholic Church officially set aside the concept of limbo as a definitive teaching. Many cilliní across the country remain without formal documentation, their locations held in local memory rather than any official record.