No earthwork rises above the field surface, no stone marks the perimeter, and the land gives little away. Yet overhead, in aerial photographs, the ghost of an early medieval settlement resolves itself quite clearly: a circular enclosure roughly 45 metres across, its outline preserved as a cropmark, the buried ditch beneath causing the vegetation above to grow and colour differently from the surrounding soil. It is a reminder that a great many of Ireland's ringforts, of which there were once tens of thousands, have been levelled so thoroughly by centuries of agriculture that only the buried traces remain.

A rath, as ringforts of this type are generally known, was typically a circular earthwork enclosing a farmstead, defended by one or more banks and ditches. The Rosspile example sits on a gentle east-facing slope in the valley of the Corock River, a stream that runs roughly north to south and would have passed some 160 to 220 metres to the east of the enclosure. The aerial photographs show a single continuous fosse, the term used for a defensive ditch, running around the full circumference, along with one internal pit. A magnetic gradiometer survey, a non-invasive geophysical technique that detects buried features by measuring subtle variations in soil magnetism, later confirmed the enclosure's existence but found no significant internal features. It did, however, identify an entrance gap on the southern side, approximately three metres wide, which would have been the point of access into the enclosed space.