On the River Suir near Ardmayle in County Tipperary, the first edition Ordnance Survey six-inch map, produced in 1840, marks a feature labelled 'Old Weir'. A weir is a low dam built across a river to raise the water level upstream, typically for milling, fishing, or controlling flow, and such structures were once common on Irish waterways. Yet when surveyors returned to update the maps in later decades, the feature had vanished from the record entirely, and nothing on the ground today corresponds to what the 1840 cartographers thought worth noting.

What makes this small absence quietly interesting is the word 'old' in the original name. By the time the Ordnance Survey teams were working through Tipperary in the late 1830s, the weir was apparently already old enough to carry that label, suggesting a structure with origins well before the nineteenth century. The mapmakers recorded it, presumably because some physical trace or strong local memory persisted, yet no subsequent edition of the OS map saw fit to repeat it. Whether the remains were cleared, eroded by the Suir's current, or simply reassessed as too slight to warrant inclusion, the record does not say. The site now exists primarily as a cartographic ghost, a name pointing to a function and a form that the river has since absorbed without leaving a readable mark.