At Killarecastle in County Westmeath, however, the curving line that swings to the north-east of the medieval church ruins may be tracing something far older: the arc of an Early Christian ecclesiastical enclosure, the roughly circular or oval boundary that once defined a sacred monastic precinct. These enclosures, common across early medieval Ireland, were often marked by a raised earthen bank or ditch, and though they can be difficult to read on the ground today, their ghost sometimes survives in the bends of later field and townland boundaries.

The site has its origins in the late sixth century, when Áed mac Bricc, also known as Hugh, is said to have founded the settlement of Killare, a name that appears in Irish as Cill Áir or Cill Fháir. The placename Ballyhugh, recorded as an alternative name for the same area, is likely a direct reference to this founder. According to early ecclesiastical records, Áed built not one but three religious structures here: St Aedh's Church, a church dedicated to St Brigid known as Temple Brigid, and a building described in Latin as an aula, meaning a hall or court, also associated with St Brigid. The presence of two Brigidine dedications alongside the founder's own church suggests a community of some complexity, perhaps with both male and female religious life, or simply a site that accumulated layers of patronage and devotion over time.

What survives above ground today are the ruins of a medieval church, and it is the relationship between that structure and the curving townland boundary to its north-east that makes the site of interest. The curve is tentative evidence rather than certainty, but it gestures towards a much earlier landscape, one in which Killare was the kind of enclosed, bounded sacred space that defined Irish Christianity in the centuries before the Norman reorganisation of the church.