Marked clearly on the first edition of the Ordnance Survey 6-inch map, this single-ringed fort has left no visible remains for modern visitors to explore. The site’s location on light grazing land suggests it was likely a cashel, a stone-built circular enclosure typical of early medieval Ireland, rather than an earthen rath.

These ringforts, which number in the thousands across Ireland, served as fortified farmsteads between roughly 500 and 1200 CE. They were the rural homes of farming families, providing protection for both people and livestock whilst demonstrating the social status of their inhabitants. The vanished fort at An Tóin Dubh would have been part of this vast network of settlements that once dotted the Irish countryside, each one a small but vital piece of the medieval landscape.

The disappearance of this particular fort remains something of a mystery, though it’s not uncommon for such structures to be dismantled over the centuries, their stones repurposed for field walls, houses, or road building. What remains is its memory, preserved in old maps and archaeological surveys, a reminder that the Irish landscape is layered with histories that aren’t always visible to the casual observer. The Archaeological Survey of County Donegal, compiled in 1983, continues to serve as an essential record of these lost monuments, documenting what once was even when the physical evidence has long since disappeared.