At Fortland in County Sligo, a cromlech, the old term for a megalithic tomb or dolmen, was recorded on the Ordnance Survey's six-inch map of 1837, labelled with quiet confidence and then, edition by edition, quietly dropped. By the time anyone looked closely at the ground, there was nothing left to map.

The scholar Seán Ó Nualláin, writing in 1989, tracked down the original map position and found that nothing survives at the spot. What he did note, perhaps more poignant than a complete absence, were a few stones sitting in a field fence to the south. They may represent the last physical remnants of the monument, absorbed into agricultural boundary-making at some point in the century and a half between the first survey and his visit. It is a fate that befell many prehistoric structures across Ireland, their carefully placed capstones and uprights gradually repurposed as convenient building material by generations of farmers with no reason to treat old stones differently from any others.