A large oval earthwork, measuring roughly 140 metres east to west and 104 metres north to south, sits in level grassland at the edge of marshy ground. It is the kind of feature that registers, if at all, as a slight rise in the turf, a gentle ridge where the land seems to gather itself. But this bank, with the remnant of an external fosse, or ditch, still visible at the south-west, marks the boundary of an early ecclesiastical enclosure, the characteristic footprint of an early Irish monastic or church site.

Ecclesiastical enclosures of this type are among the more quietly persistent features of the Irish landscape. Typically circular or oval in plan, they defined the sacred boundary of an early Christian settlement, separating the religious community and its associated structures from the surrounding land. The Shantallow enclosure survives in fair condition, though a field wall has been built directly over the bank along much of its southern arc, running from the east around through to the north-west. The fosse that once accompanied the bank has largely disappeared, surviving only at the south-west. Gaps at the north-east and west are thought to be modern breaks rather than original entrances. Associated with the enclosure is a burial ground, which suggests that whatever community once gathered here left more than earthworks behind.