No earthwork rises from the ground, no stones mark a perimeter, and nothing alerts a passing eye to the fact that anything of significance ever stood here. The only evidence that something once occupied this small hillock in open grassland comes from a single cartographic moment: the 1838 edition of the Ordnance Survey six-inch map, which records a circular enclosure roughly twenty metres in diameter. After that, the record goes quiet.

Circular enclosures of this kind are a familiar, if poorly understood, feature of the Irish landscape. They range from the elaborate ringforts that survive in their thousands across the country to much slighter, older arrangements whose original purpose, whether domestic, ritual, or agricultural, can rarely be determined without excavation. At An Carn Mór Thiar, even the 1838 cartographers captured a site already partially compromised: a field boundary was running through the enclosure from the south-southeast to the south-southwest, suggesting that by the early nineteenth century the structure had lost whatever authority once kept farmers from building across it. At some point after that survey was made, it disappeared from the surface entirely. Today, the M6 motorway passes approximately thirty metres to the north of the hillock, carrying traffic east to west at speed, largely indifferent to what lies just beside it.