At Knocknadaula in County Galway, a south-facing slope of grassland holds what remains of a rath, the Irish term for a ringfort, the type of enclosed farmstead built in the early medieval period that once dotted the Irish countryside in their tens of thousands. What makes this particular example unusual is not what survives but the story told by comparing two maps, decades apart, of something steadily disappearing.

The Ordnance Survey's six-inch map of 1838 records a circular enclosure approximately twenty-four metres in diameter, a respectable size for a rath, suggesting a well-defined earthwork still legible in the landscape at that point. By the time the more detailed 1:2500 survey was carried out between 1912 and 1916, the record had shrunk dramatically: the same feature appears now as a small mound only around six metres across. Something in the intervening decades, whether agricultural activity, stone-robbing, or simple erosion, had reduced a substantial enclosure to a fraction of its former footprint. When inspectors visited the site in more recent times, even that modest mound had yielded little, with only a low rise in the ground remaining as any kind of surface trace. A field wall to the east of the site curves around it in a gentle arc, the kind of detail that sometimes indicates a farmer working around an older feature rather than through it, acknowledging the presence of something without quite knowing what it once was.