At Coolbeg in County Galway, there was once a rath, a type of early medieval ringfort typically consisting of a raised circular enclosure defined by earthen banks and ditches, which would have served as a farmstead or defended homestead for a family of some local standing. By the time anyone thought to look for it properly, it was already gone.

The Ordnance Survey's six-inch map of 1838 recorded it as a subcircular embanked enclosure, measuring roughly 41 metres north to south and 37 metres east to west, a substantial feature in the landscape. By the time of the revised mapping carried out between 1946 and 1947, something had already changed: what the earlier surveyors described as an enclosure had shrunk, in the cartographic record at least, to a circular mound of around 25 metres in diameter. A field boundary running north to south had clipped the eastern edge of the site, suggesting that agricultural reorganisation had been eating into it incrementally. When the site was visited in April 1983, no visible surface trace survived at all. Within roughly 150 years, a feature prominent enough to be mapped with reasonable precision had been entirely absorbed back into the farmed landscape.