In a pasture at Ardgoul South, County Limerick, there is a ringfort that no longer exists, or at least no longer exists above ground. When surveyor Denis Power inspected the site, he found nothing: no earthwork, no raised lip of soil, no surviving arc of bank to suggest that anything had ever been here at all.

What Power was looking for, based on the 1841 Ordnance Survey six-inch map, was a semi-circular embanked enclosure roughly twenty metres in diameter, sitting on the south-east side of a south-west to north-east field boundary on a gently sloping, west-south-west-facing hillside. A rath, as this type of monument is often called, is an early medieval farmstead enclosed by one or more earthen banks and ditches, used for both settlement and the protection of livestock. They are among the most common archaeological monuments in Ireland, with tens of thousands recorded across the island, though a great many have been damaged or destroyed by agricultural improvement over the centuries. This one appears to have been levelled entirely, its bank absorbed back into the surrounding pasture at some point between the nineteenth century and the time of Power's inspection, which was uploaded to the record in August 2011.

There is, practically speaking, nothing to see here now, and that is rather the point. The field in Ardgoul South looks like any other patch of Limerick farmland, a gentle slope, grazing grass, a field boundary running through. But the 1841 map records what was once there with enough precision to place it, and the gap between that document and the empty ground today is itself a kind of historical fact. For anyone interested in how the Irish landscape has been quietly reshaped by generations of farming, cross-referencing the old OS six-inch maps with what actually survives on the ground can be a surprisingly instructive exercise, even when, perhaps especially when, the monument itself is gone.