What remains is essentially a ghost recorded in cartography, a place whose existence is easier to trace through old maps than through anything visible on the ground.

A ringfort, for the unfamiliar, is a roughly circular enclosed settlement, typically dating from the early medieval period, defined by one or more earthen banks and ditches. The site at Treanybrogaun sits on a prominent hill with wide views across undulating pastureland and a stretch of bog to the east-southeast, with ground falling away to a stream some thirty metres to the west. When the Ordnance Survey mapped the area in 1838, it appeared as a circular enclosure measuring roughly twenty-five to thirty metres in diameter, with a road on a northeast-southwest axis cutting directly through its centre. By 1929, the same survey was already annotating it as "Trean Fort (site of)", and what had been a coherent enclosure was now represented only as a polygonal arrangement of field fences flanking either side of that road. When the site was inspected in 1996, those field fences were still in place, enclosing a subcircular area of up to thirty-nine and a half metres across, which likely preserved something close to the original outline. Since then, the fences have been levelled. Farm buildings now cover the eastern portion of the enclosure, and there is no visible trace of the western half in the adjoining field.

What is quietly compelling about this place is the pace of its disappearance. Between 1838 and 1929 it went from a named fort to a "site of"; between 1996 and the present it lost even the residual geometry that the field boundaries had preserved. The hill and the view remain, and the road still passes through where the enclosure once stood, but the structure itself has been thoroughly reclaimed.