These sites, known in Irish as cillíní (singular cillín), were used for centuries to inter unbaptised infants and others who, under Catholic doctrine, could not be buried in consecrated ground. They occupy a liminal category: not quite sacred, not quite secular, and often found at the margins of townlands, beside old earthworks, or on the edges of bogs and fields. Their presence is easy to overlook, and many have no formal monument or marker.

The use of cillíní was shaped by a theological position, rooted in the doctrine of limbo, which held that unbaptised children could not enter heaven. This placed grieving families in a difficult position, excluded from the usual rites of burial and forced to find other ground. In practice, communities across Ireland quietly maintained these peripheral plots for generations, the knowledge of their location passed down locally rather than recorded in any official way. The Lettera site sits within this broader pattern, a small piece of ground in the west of Mayo carrying the weight of that long, unofficial history.