The ringfort at Killynan in County Westmeath is one such case. A ringfort is a roughly circular enclosure, typically of the early medieval period, defined by an earthen bank and an outer ditch; thousands survive across Ireland in varying states of preservation. This one, sitting on a low rise in gently undulating pasture, had already been recorded and mapped before it was gone, which is the only reason we know much about it at all.

The site appears on the 1837 Ordnance Survey Fair Plan simply annotated as "Fort", and by the time the revised 25-inch map was drawn up in 1913 it was recorded as a suboval earthwork roughly 28 metres north to south and 30 metres east to west, defined by a scarp (an abrupt slope or edge in the ground) and an outer fosse, the ditch that would originally have reinforced the enclosure's boundary. When the monument was described in January 1970, that basic form was still legible, though digging had already damaged the scarp and fosse on the south-east. By March of the same year, just weeks later, it had been levelled entirely. What remained was a cropmark, the kind of ghost that only aerial photography or a dry summer can reveal: a roughly circular area of dark brown earth approximately 52 metres in overall diameter, with only a very shallow curvilinear depression, some 7 metres wide and barely 20 centimetres deep, tracing the arc of the old fosse from the south-west around to the north. Today, even that faint trace has vanished from aerial imagery.

The gap between the 1913 map and the 1970 descriptions is itself telling. For most of the twentieth century the earthwork persisted, probably unremarkable to anyone passing through the surrounding farmland. The damage and subsequent levelling within the space of a single winter point to the kind of agricultural improvement that reshaped so many Irish fields during that period. What the 1837 surveyors marked without ceremony, and what cartographers still showed half a century later, is now recoverable only through the sequence of records it happened to leave behind.