A circular enclosure, somewhere between twenty and twenty-five metres in diameter, was recorded on the Ordnance Survey's six-inch map of 1838, sitting on a level platform with the land dropping away sharply to the west. By the time later map editions were produced, it had disappeared from the cartographic record entirely, and today there is no visible trace of it at ground level whatsoever. In its place: pasture, a minor road running north to south, a vegetable garden, and a concrete cattle crush.

Circular enclosures of this kind are a familiar feature of the Irish countryside, appearing in many forms across many periods, from early medieval ringforts used as farmsteads to prehistoric ceremonial sites. What makes the Shantallow example quietly compelling is precisely its elusiveness. The 1838 survey was an extraordinarily detailed exercise, the first large-scale systematic mapping of Ireland, and its field surveyors were generally reliable recorders of earthworks visible in their time. That something was there in 1838 and then gone from subsequent maps suggests either that the feature was already faint and was not consistently noted, or that the ground was disturbed or levelled in the intervening decades. The ridge-top position, with its extensive westward views, is the kind of location that tends to attract human activity across long stretches of time, which makes the absence of any surviving trace all the more pointed.