It surfaces, in a sense, only on paper: the 1838 Ordnance Survey six-inch map records it with hachures, the fine radiating lines cartographers used to indicate raised earthworks or earthen banks. That notation suggests a defined, enclosed space, the kind of circular earthwork found across Ireland in various periods, sometimes a ringfort marking a farmstead boundary, sometimes something older and harder to categorise. Whatever its original function, it now belongs to the reservoir rather than to the landscape.

Vartry Reservoir was constructed in the 1860s to supply Dublin with fresh water, flooding a stretch of the Vartry valley and permanently altering the ground beneath. The enclosure at Knockatemple was among the features swallowed by that inundation. Its existence was confirmed through a visit made during low water following a dry summer, when the receding waterline occasionally exposes what ordinarily remains hidden. Even then, nothing was visible at ground level; its presence is documented rather than directly observable, known through the cartographic record made nearly three decades before the reservoir changed everything above it.