Known in Irish as Seana-Droichead na Gairfeanaighe, it is a drystone bridge, meaning it was assembled without mortar, relying entirely on the weight and arrangement of its stones to hold together. That it continues to hold together at all is quietly remarkable.

The bridge is reputed to be medieval, though its precise age remains uncertain. Built from local stone, it rests on foundation bases constructed from very large stones on either bank, with further stones set back on those bases at angles calculated to push against the outward force of the arch above. This counteracting of thrust is the essential logic of arch construction, and here it was achieved without dressed stonework or binding agents of any kind. The arch itself is slightly pointed rather than fully rounded, and the bridge curves gently on plan rather than crossing the river at a right angle. At the crown of the arch, the tops of the central voussoirs, the wedge-shaped stones that lock an arch in place, actually form the road surface itself. Elsewhere the carriageway is paved with large smooth stones and patches of rounded cobbles. At 1.65 metres wide, it was narrow enough that vehicles could only ever cross in a single direction at a time, the low parapets on either side kept deliberately modest so as not to waste any of that limited width.

The bridge is a designated National Monument and has undergone repair and conservation works. It sits just downstream from its modern replacement, which means that with a little attention to the riverbank, both crossings are visible in the same glance, the old and the new occupying the same corridor through the landscape with no particular ceremony between them.