These sites, known in Irish as cillíní (the singular is cillín), were informal burial places used for unbaptised infants, and sometimes for others considered to exist outside the formal rites of the Catholic Church, including stillborn children, victims of suicide, and strangers whose origins were unknown. Because the Church denied such individuals consecrated ground, families buried them instead in liminal spaces: old ring forts, the edges of fields, shorelines, and ancient or disused ecclesiastical sites. The ground was not sanctioned, but it was chosen with care, often carrying its own quiet gravity.

Cillíní were used across Ireland from at least the medieval period and continued well into the twentieth century. The practice reflected a painful intersection of religious doctrine and human grief, with parents finding their own form of sacred space when the official one was closed to them. Many cillíní in Connacht occupy locations with earlier archaeological significance, which may reflect a folk belief that old, pre-Christian ground retained a kind of holiness independent of Church authority. The site at An Cheathrú Mhór is recorded as a monument, placing it within a broader landscape of such burial grounds that are gradually receiving the archaeological and historical attention they long lacked. For much of the twentieth century, cillíní were rarely spoken of openly, their locations passed down in families or quietly forgotten, and only in recent decades has serious effort gone into documenting them as places of social and emotional, as well as archaeological, significance.