The 1838 six-inch map shows a complete circular embanked enclosure at Tullanacorra in County Mayo; by the 1931 edition, the southeastern portion had been levelled, and the map records only a semicircle, its missing arc replaced by a field boundary running northeast to southwest. That boundary is still there, bisecting what remains of the interior. It is the kind of gradual, undramatic erasure that happens across Irish farmland over generations, each adjustment to a field system trimming a little more from something that was already ancient.

A rath, the Irish term for a ringfort, was typically a circular or oval enclosure defined by an earthen bank and ditch, used as a farmstead during the early medieval period, roughly between the fifth and twelfth centuries. The Tullanacorra example sits on gently rising ground, with the land falling away to the west and north into a natural basin of damp pasture, and a ridge rising to the south-southwest. What survives today is a broadly oval area, approximately 28 metres along its northeast-southwest axis and 23 metres across, defined on its northwestern half by a scarp that still stands around 1.4 metres high at its best-preserved point to the west. Towards the northeast and southwest ends of its arc, the bank diminishes, and along the northeast-to-south stretch it has been reduced to a barely perceptible rise in the ground. Within the northwestern quadrant of the interior there is a souterrain, an underground stone-lined passage or chamber associated with early medieval settlement, used variously for storage, refuge, or ventilation. Notably, both the 1838 and 1931 OS maps marked this feature simply as "Cave", suggesting it was a locally recognised curiosity long before it was formally recorded.