At Holdenstown in County Wicklow, a rectangular enclosure sits on the edge of a ridge above a steep north-east-facing slope, and yet a person standing on the very ground it occupies would see nothing. No earthwork rises from the soil, no ditch catches the eye, no obvious boundary marks one piece of land from another. The enclosure is, to all appearances, invisible.

What makes this site legible at all is the 1838 Ordnance Survey six-inch map, one of the most detailed cartographic exercises ever carried out in Ireland, which recorded the enclosure's outline at maximum dimensions of roughly 40 metres by 45 metres. An enclosure of this type would generally refer to a defined area bounded by an earthen bank, a wall, or a ditch, sometimes associated with early medieval settlement, agriculture, or ritual use, though the specific function of this one is unknown. By the time archaeologists came to examine it at ground level, whatever once made it visible had been reduced, by ploughing, erosion, or simply time, to nothing detectable without the old map as a guide. The ridge position is itself suggestive; elevated ground overlooking a pronounced slope was a favoured location for enclosures of various periods in Ireland, offering both outlook and a degree of natural definition to the site.