Roughly thirty centimetres high and forty-five wide, with a carefully worked external chamfer along its curved edge, it is all that remains visible of a medieval church that once stood on this ground. The fragment most likely served as a window head, or possibly as part of a piscina or stoup, the piscina being a shallow basin used for draining water from liturgical vessels, the stoup a vessel for holy water near a church entrance. It was built into the east face of the western kerb wall when the older building was cleared away, a quiet act of preservation, or perhaps simply convenience.

The church in question was dedicated to St. Nicholas of Myra, the same fourth-century bishop of Lycia whose cult spread widely across medieval Europe and whose name is carried by dozens of Irish parish churches. According to O'Flanagan, writing in 1930, the medieval structure appears to have survived until around 1813, when it was demolished to make way for the Church of Ireland building that now occupies the site. The chamfered limestone fragment is among the only physical traces of that earlier building still in place, absorbed into the fabric of its successor rather than discarded.