It is, in all likelihood, far older than either the wall or the church beside it. The embankment, roughly seven metres wide and just forty centimetres high, is thought to be a remnant of an ecclesiastical enclosure, the kind of curving boundary that early Irish monastic communities used to define sacred space. These enclosures, typically oval or circular in plan, are one of the clearest indicators of a pre-Norman Christian site, often predating the introduction of the parish church system to Ireland after the twelfth century.

The earthwork was first formally noted by Swan in 1971, who identified not just the single bank to the northwest of the church but evidence of a double enclosure extending from the southwest to the northeast, running close to the curving roadway adjacent to St David's. That curving road itself is worth pausing over: in many early ecclesiastical sites across Ireland, the local road network preserves the arc of the original enclosure long after the earthwork has eroded or been ploughed away. A later aerial study, published by Clinton in 2005, confirmed a low curving bank enclosing the churchyard to the north and east, adding further definition to what Swan had outlined on the ground. Taken together, the evidence points to a layered site where early medieval activity preceded the standing medieval church fabric.

The enclosure is visible on the Bird's Eye view in Bing Maps, which gives a useful sense of its outline before visiting. On the ground, the experience is more ambiguous. The area has been fenced off as a horse enclosure and, at the time of the most recent site notes, the ground had been heavily poached by hooves, meaning the subtle topography of the earthwork is obscured by churned soil. Visitors hoping to read the landscape will need patience and a good eye for slight changes in ground level. The site is best assessed from the roadside or by studying aerial imagery rather than by walking the earthwork directly.