At Ballyduff More in County Clare, it appeared to do exactly that, showing what looked like a circular enclosure of the kind found across Ireland in their thousands. The only problem was that it was not one.

The site never made it into either the Sites and Monuments Record of 1992 or the Record of Monuments and Places of 1996, which together form the backbone of Ireland's statutory heritage inventory. When someone eventually walked the ground in 2002, the explanation turned out to be entirely geological. What the aerial images had captured was a natural rise in the landscape, with no banks and no fosses, the ditches that typically define a man-made enclosure. The circular outline was simply a broad band of rushes growing around the base of the mound, the kind of wet-loving vegetation that colonises low-lying, poorly drained ground. At the centre of it all was a quarry, unremarkable in itself, but quietly responsible for one of the more modest misidentifications in the Clare record.

The episode is a small illustration of how misleading the view from above can be. Shadows, seasonal vegetation, and slight variations in ground moisture can conspire to suggest archaeology where none exists, and the only reliable correction is still a pair of boots on wet grass.