At Castlewilder in County Longford, a small circular earthwork sits on a low rise in well-drained pasture, its presence confirmed by maps rather than by the eye. Standing at its location, a visitor would have no particular sense of anything beneath or around them, yet the feature is real enough to have been recorded and measured, with a base diameter of roughly fifteen metres.

What makes its history stranger still is the question of when it entered the cartographic record. The Ordnance Survey mapped Ireland in remarkable detail from the 1830s onward, and the six-inch maps of 1837 and 1883 show no trace of this mound at all. It appears for the first time on the 1914 edition, depicted as a small circular feature. Whether it was overlooked in the earlier surveys, had been partially levelled and later survived, or simply escaped notice on two separate occasions, the record does not say. Mounds of this general type in the Irish midlands can belong to a wide range of periods and purposes, from prehistoric burial cairns to medieval earthworks associated with ringforts or moated sites, though nothing in what is known about this particular example ties it firmly to any one category.