What gives it away is a cropmark, the subtle variation in how grass or grain grows above buried features, where a filled-in ditch causes vegetation to behave differently from the soil around it. In this case, the buried feature is a fosse, a defensive or boundary ditch, tracing a curvilinear path that would once have defined the edge of an enclosure.

This kind of enclosed site is a familiar if still poorly understood feature of the Irish landscape. Curvilinear enclosures of this scale are broadly associated with early medieval settlement, often the remains of a rath or ringfort, where a circular area was enclosed by one or more banks and ditches to demarcate a farmstead or place of habitation. What survives at Barrettsgrange survives only as a ghost. The fosse has long since been ploughed or silted into invisibility, and the enclosure itself leaves no surface trace. Its existence was captured in a single aerial photograph, taken in 1990, in which the cropmark traced the circuit of the old ditch across the field below.