At Ardnaglen in County Westmeath, it is the shape of the boundary wall surrounding the graveyard that has drawn attention. Rather than the straight lines of a later, more utilitarian enclosure, the wall follows a distinctly oval course, and it is this form that has led researchers to suspect something earlier and more deliberate lies beneath the surface of the site.

In early medieval Ireland, ecclesiastical settlements were frequently defined by a roughly circular or oval enclosing boundary, known as a cashel if built in stone or a rath-like earthwork if raised in earth and timber. These enclosures marked out sacred ground, separating the monastic community or church site from the secular landscape around it. Many such enclosures were absorbed into later parish graveyards, their original boundaries gradually rebuilt in drystone or mortar over the centuries, but their characteristic rounded outline surviving into the present. At Ardnaglen, the researcher Leo Swan noted in 1988 that the oval form of the graveyard wall was consistent with this pattern, raising the possibility that the site represents the remnant of an early ecclesiastical enclosure whose origins may stretch back to the early Christian period in Ireland.