These variations in colour and height, known as cropmarks, form when buried ditches or walls affect the soil's moisture and nutrients, causing the plants rooted above them to ripen faster or slower than their neighbours. Seen from the air at the right moment in the growing season, the ghost of an ancient enclosure emerges. A wide ditch, or fosse, traced this particular circle, and on one photograph an apparent gap in the eastern quadrant hints at where an entrance once stood.

The enclosure came to light through aerial photography carried out in the summers of 1969 and 1971, with a further image taken in 1995 adding detail about the eastern break in the fosse. What makes Rathclogh particularly striking is not just the single site but the cluster it belongs to. At least four other enclosures have been identified in the immediate area, most of them also visible only as cropmarks. The nearest sits just 20 metres to the south; others appear at roughly 70 metres, 140 metres, 190 metres, and 220 metres from this one, spread across a compact arc of landscape. Only one of the group appears to survive as an earthwork above ground. Such concentrations of enclosures are not unusual in the Irish midlands and south-east, where ringforts and related settlement forms were built in considerable numbers during the early medieval period, roughly the fifth to twelfth centuries, though without excavation it is difficult to assign a precise date or function to any individual site.