The ringfort at Coolnanoglagh, in County Limerick, does the opposite. It has, to all appearances, ceased to exist. Stand in the level pasture where it ought to be, and there is nothing to see.

A ringfort, or rath, is one of the most common monument types in the Irish landscape, a circular enclosure defined by an earthen bank and ditch, typically dating from the early medieval period and used as a defended farmstead. They number in the thousands across the country, and their low, rounded profiles have survived in fields and hillsides for over a thousand years. The example at Coolnanoglagh was recorded on the Ordnance Survey six-inch map of 1840 as an embanked circular enclosure roughly thirty metres in diameter, mapped with the careful attention the OS brought to earthworks during that great nineteenth-century survey of Ireland. Compiled by Denis Power and uploaded to the record in August 2011, the site entry notes plainly that there is now no evident surface trace of the monument. Whatever the 1840 surveyors observed has since been levelled, most likely by agricultural activity in the intervening century and a half.

For a visitor, this is a site that rewards a particular kind of curiosity, the kind drawn not to spectacle but to absence. The location sits in ordinary farmland, and without the original OS map for comparison there is little to orient yourself by. The 1840 six-inch sheets are freely accessible through the Historic Environment Viewer and similar online mapping tools, which allow you to overlay the old survey on modern satellite imagery and locate, more or less precisely, where the enclosure once sat. What you find at the spot itself is grass, and the faint knowledge that somewhere underfoot the banks were graded flat, the ditch filled in, and a small early medieval world was quietly erased from the surface of the land.