Not dramatically collapsed, not submerged, not quarried away, but quietly eroded by the slow creep of agriculture until nothing remains above ground at all. The site at Knockballyvishteal is, in the most literal sense, an absence where a presence once was.

Ringforts, the circular enclosed farmsteads of early medieval Ireland, were once scattered across the landscape in their tens of thousands. They typically comprised an earthen bank and internal ditch enclosing a domestic space. The one at Knockballyvishteal sat on a glacial ridge, with bogland to its north-east and south, and was substantial enough in its prime: a diameter of roughly 35 metres, with a scarp, the steep outer face of the earthen bank, standing about 1.8 metres high. When Neary wrote it up in 1914, citing it as entry no. 148 in his survey, he described it as a "circular, earthen, half ravelled fort" whose interior garth, the enclosed yard, measured over 100 feet across. Even then, tillage operations had already begun eating into it. The fort was known locally as Concannon's Fort, a name that preserves something of its social memory even as the physical structure was disappearing. It was recorded on the first edition of the Ordnance Survey six-inch map as a roughly circular enclosure, which gives at least a paper trace of what once stood there.

Today, no visible surface trace survives. The glacial ridge is grassland, flanked by bog, and there is nothing underfoot that would announce itself to a passing walker. What remains is essentially cartographic and archival, a shape on an old map, a paragraph in a 1914 publication, a local name that may or may not still circulate among people nearby.