It is a cillín, the Irish term for an unconsecrated burial site used for unbaptised infants, and its presence here speaks to a practice that was once widespread across rural Ireland but is only now beginning to receive serious historical attention.

For centuries, Catholic doctrine held that unbaptised children could not be buried in consecrated ground. Families, unwilling to leave their infants without any form of burial, instead used marginal or liminal spaces, old earthworks, the edges of fields, or sites with a pre-Christian association. These places became known as cilliní, and they exist in their hundreds across the Irish landscape, often unmarked, often unrecorded in any official sense, and almost always carrying the particular quietness of grief that has nowhere formal to go. Slievemore itself has long been associated with older layers of habitation; the deserted village at its base, abandoned during and after the Famine years of the 1840s, is among the most affecting archaeological landscapes in Connacht. A cillín in this vicinity fits a pattern seen across the west of Ireland, where marginal land, difficult terrain, and the long memory of pre-Christian sacred geography all converged.

The mountain is accessible from Dugort on the north of Achill Island, and the deserted village below it is a well-known site in its own right. Visitors who walk the slopes may pass the cillín without recognising it for what it is; these sites rarely announce themselves, and that is rather the point.