Circular ecclesiastical enclosures are generally understood to mark the footprint of early Christian monasteries, the curved boundary wall preserving the memory of a community that stood here long before any documentary record caught up with it. In this case, the monastery in question is thought to have been associated with two early Irish saints, Faolan and Carthage Mochaeda, and the ground they hallowed has never entirely stopped being used.

The place-name Kiltallagh derives from Cill Tulach, meaning something like 'the church of the hill', and the site sits within the diocese of Ardfert, barony of Trughanacmy. By 1302, it was significant enough to appear in papal taxation records for the Deanery of Offeria, where the church of 'Kiltulagh' was valued at 13 shillings and 4 pence annually, with a tithe of 16 pence. Writing in 1893, O'Donoghue suggested that this was the very church from which St Carthage Mochaeda had once been forced to withdraw, with Bishop Domaingen later placing his brother Faolan in charge. A Church of Ireland building now occupies what is almost certainly the site of that medieval structure, dedicated to St Carthach, and a 19th-century account noted that scattered stones from the earlier building were still visible around the graveyard. One of those stones is anything but scattered: a hollowed stone, shaped like an inverted cone, known as Cloch Mochaeda, the stone of St Carthage Mochaeda. A folklore account collected from Castlemaine School, probably in the late 1930s, describes people arriving at the stone before dawn, bringing water from a nearby well, saying several rosaries, and washing their eyes in the water in hope of a cure. They left rags or tokens on a tree beside it, a practice common at Irish holy wells, and tradition held that touching one of those rags would pass on whatever affliction the previous visitor had sought to shed. The schoolchild who recorded this added, almost in passing, that on dark winter nights a large light was seen among the ruins, and that three priests were said to be buried at the centre of the old church.