At Knockbrack in County Limerick, a ringfort, the type of circular earthen enclosure, typically defended by a bank and ditch, that served as a farmstead during the early medieval period, has been entirely erased from the landscape. Where there was once a structure, there is now only pasture on a steep west-south-west-facing slope, with no trace of the monument remaining.

The ringfort at Knockbrack was still visible, at least as a cartographic feature, when the first edition Ordnance Survey six-inch map was produced in 1841. That survey recorded it as an embanked circular enclosure of approximately thirty metres in diameter, a fairly typical size for a rath of its kind. A rath is simply the Irish term for this class of earthwork, built up using excavated material to form a surrounding bank. At some point between that 1841 survey and the inspection carried out by Denis Power, the monument was levelled, most likely through agricultural improvement or land clearance. When Power visited the site, he found nothing to indicate anything had ever been there.

For anyone curious enough to seek out the location, the site sits in farmland on a pronounced slope, so access would require landowner permission and the terrain itself is not especially forgiving. There is nothing visible to reward the visit in any conventional sense. What makes the journey worthwhile, if anything does, is precisely that absence, the knowledge that the map once showed something here, that early medieval people chose this particular hillside, and that the record of it now exists only in an OS sheet from 1841 and a brief note compiled in 2011. The coordinates exist; the monument does not.