It betrays itself only from the air, as a cropmark, the phenomenon whereby buried ditches and banks influence how plants above them grow, producing faint differences in colour and height that become legible in aerial or satellite photography. In this case, the enclosure takes an oval form, roughly 29 metres along its northwest to southeast axis and around 24 metres across, defined by a fosse, which is simply a ditch dug to demarcate or defend a space. The shape is consistent with the kind of enclosed settlement or farmstead that appeared across Ireland during the early medieval period, though the ground at Knockanacree gives nothing away to someone standing in the field.

The site was identified and reported by Jean-Charles Caillère, working from satellite imagery available through Apple Maps, a reminder that some of the most useful archaeological prospection now happens at a desk rather than in a trench. The first edition six-inch Ordnance Survey map, produced around 1840, adds a small detail: it marks an area of quarrying immediately to the west of the enclosure. That disturbance is still faintly legible on the satellite imagery as a dark stain in the soil, a trace of nineteenth-century extraction sitting alongside traces that are likely a great deal older. The two marks, one prehistoric or early historic, the other industrial, occupy the same field without either one fully erasing the other.