But that curving earthwork, visible only in fragments, is likely the surviving trace of an early ecclesiastical enclosure, the kind of roughly circular boundary that once defined the sacred precinct of an early Irish monastic or church site. Such enclosures, sometimes constructed as a fosse (a defensive or demarcating ditch), sometimes as a cashel-type wall of dry stone, were a standard feature of early medieval religious settlements across Ireland, marking the boundary between the secular world and consecrated ground.

The enclosure at Abbeytown came to wider attention during aerial reconnaissance in January 1985, when a strongly curving fosse-like feature was spotted to the north of a possible church site. Photographed from the air, it appeared to arc from the west-northwest through north to northeast, with a diameter of roughly 140 metres when centred on the church. On the ground, the feature is considerably harder to read; it has been much defaced over time and is overlain by a later field system. Along its inner, southern edge, intermittent traces of a stony bank survive. Researchers Higgins and McHugh, writing in 1990, recorded what is almost certainly the same feature to the northeast of the church, describing it as the remains of a substantial stone wall standing to a maximum height of between 0.33 and 0.40 metres, with traces of an external wall facing still discernible. That combination of a fosse and a stone wall with facing stones points to a carefully constructed boundary rather than a casual field boundary, and aligns well with what is known of cashel-type enclosures associated with early church sites elsewhere in Connacht.