At Drumbeo in County Monaghan, a circular enclosure was recorded by a cartographer named Willoughby on a map of the Ballybay estate in 1786, drawn with enough confidence to suggest he was depicting something real. Yet aerial photography reveals nothing at ground level, no crop mark, no soil discolouration, no earthwork remnant. The feature has effectively vanished, leaving only its ink outline behind.

The site sits in a slight col, the shallow saddle of land between a low rise roughly a hundred metres to the west and a taller drumlin climbing away to the northeast. Drumlins, the smooth oval hills shaped by glacial activity that give much of Monaghan its rolling, hummocked character, would have made this kind of sheltered dip a natural focal point in the landscape. Whether the enclosure Willoughby recorded was a ringfort, a field boundary, or something else entirely is complicated further by a discrepancy in the early maps. The 1834 edition of the Ordnance Survey six-inch map marks a feature described as "Rocks" a short distance to the north of this location, and it is possible the two records refer to the same thing, shifted slightly, misidentified, or simply described differently by two different observers nearly fifty years apart. Circular enclosures in Ireland most commonly take the form of ringforts, which were enclosed farmsteads typically dating from the early medieval period, though they were in use across a broad span of centuries.