These grounds, known in Irish as cillíní (singular: cillín), were used for centuries to inter those who died unbaptised, most often infants, but sometimes also stillborn children, women who died in childbirth, and others considered to exist outside the formal rites of the Catholic Church. Because unbaptised souls were held, under older theological doctrine, to be excluded from consecrated ground, families buried their children in these separate, liminal places instead: old ringforts, the margins of bogs, the edges of fields, or sites associated with early Christian enclosures. The practice was widespread across Ireland and continued well into the twentieth century in some areas.

An Tinbhear, the Irish name suggesting a confluence or estuary, is a townland in Mayo, a county where cillíní are relatively well documented across the landscape. The specific history of this particular ground, including when it was established, how long it remained in use, and whether it is associated with any earlier ecclesiastical or prehistoric site, is not currently available in the accessible record. What can be said is that sites of this kind are rarely marked with formal headstones; they are more often indicated by small field stones, slight undulations in the ground, or by local memory passed down through generations. Many remained unknown to anyone outside the immediate community for decades, their locations held quietly by families who had buried children there under circumstances that combined grief with social stigma.