In a gently rolling patch of grassland in Tonrevagh, North Galway, just to the south-east of a small pond, there once stood a rath, a type of circular earthen enclosure used in early medieval Ireland as a farmstead or seat of local authority. It measured roughly thirty metres across, which is a modest but entirely typical size for such structures. Today, nothing of it can be seen at ground level. The field offers no bank, no ditch, no crop mark visible to the casual eye. The site exists, in any meaningful present-day sense, only because someone recorded it before it disappeared.

That record comes from the first edition of the Ordnance Survey six-inch map, the remarkable nineteenth-century cartographic project that swept across Ireland in the 1830s and captured countless archaeological features that were already fading from the landscape. On that map, the Tonrevagh enclosure appears as a circular form, enough for later researchers to identify it as a probable ringfort. Raths were the most common type of settlement in early medieval Ireland, typically consisting of a raised circular area enclosed by one or more earthen banks and ditches, and used by farming families across a period stretching roughly from the fifth to the twelfth century. Thousands survive in varying states across the country; many thousands more have been levelled by ploughing, land improvement schemes, or simple neglect over the intervening centuries. The Tonrevagh example belongs to the latter category.