On a south-facing slope in the pastureland of Mannin, Co. Galway, a circular cashel, the Irish term for a stone-walled ringfort, once measured roughly 28.6 metres in diameter. By the time surveyors visited in May 1983, the drystone enclosing wall had largely collapsed, and along the northern arc a farm shed and concrete yard had been built directly on top of what remained. When they returned in June 1992, the cashel itself had been levelled.

What made the site more complex than a simple enclosure was the accumulation of features recorded around and within it. A scholar named McCaffrey, writing in 1952, had noted the presence of a souterrain, an underground stone-lined passage typically associated with early medieval settlement and used variously for storage or refuge, as well as an oval annexe extending north of the main wall. This outer enclosure, defined by a wall of mixed earth and stone, measured approximately 44 metres by 28.5 metres. Traces of a house site were also recorded in the eastern interior. By 1983 none of the souterrain, the annexe, nor the house site retained any visible surface trace, meaning that even before the final levelling, much of the structural complexity McCaffrey had observed three decades earlier had quietly disappeared into the ground or been absorbed by the working farm around it.

The Mannin cashel is a useful, if sobering, example of how quickly an early medieval site can move from poorly preserved to entirely gone within a single generation. Its loss is not dramatic; there was no single event, just the slow pressure of agricultural use and infrastructure gradually overwriting a landscape that had probably been farmed continuously for over a thousand years.