At Knocknalyre in County Cork, what was once a substantial ringfort, a circular earthen enclosure of the kind built throughout Ireland from the early medieval period onwards as a farmstead or high-status residence, has been worn down so thoroughly by centuries of grazing that its clearest surviving feature is a stripe of thistle growth cutting across the pasture. That line of weeds marks the course of the original fosse, the external ditch that once helped define and defend the enclosure's perimeter.

Ordnance Survey maps from 1842, 1904, and 1937 all show the site as a hachured circular enclosure roughly forty metres in diameter, with the 1937 edition also picking out the external fosse with hachures. By the time a ground survey was carried out, the structure had been largely levelled. What remained was a roughly circular area measuring about thirty-six metres east to west and thirty-five metres north to south, enclosed on the west, north, and east sides by a low undulation reaching no more than 0.4 metres in height. Outside that, the thistle line traces the fosse from the west-northwest to the southeast, and there is a suggestion of a second bank beyond it, surviving as a further gentle rise of around 0.3 metres. It is the kind of site that asks something of the eye, where the map record becomes almost more legible than the ground itself.

The OS map sequence is particularly useful for understanding what has been lost. Between 1842 and 1937 the basic outline remained recognisable enough to be consistently recorded; what disappeared happened largely after that, probably through agricultural improvement and repeated ploughing or heavy stock pressure. The thistles, opportunistic as they are, have inadvertently preserved the memory of the ditch by colonising the disturbed or wetter ground where it once ran.