These sites, known in Irish as cillíní (singular: cillín), were used for the interment of unbaptised infants and others considered ineligible for burial in consecrated ground, including stillborn children, and occasionally adults who had died by suicide or outside the formal structures of the Church. They occupy a liminal space in every sense, neither fully sacred nor wholly secular, and they tend to appear at the margins of parishes, on townland boundaries, near ringforts, or on old, pre-Christian ground.

The use of cillíní in Ireland spans many centuries, though the practice was most prevalent from the medieval period through to the early twentieth century, when Church teaching on baptism and the fate of unbaptised souls shaped funeral customs in ways that could leave grieving families without recourse to official burial rites. Parents often interred their children at night and in silence, without ceremony, in places that carried their own older sanctity. The Callow site in Mayo is one of hundreds recorded across the country, each one a quiet marker of a practice that was, for generations, both common and rarely spoken about openly.