This is a togher, the Irish term for a timber trackway laid across wet or boggy ground, and it represents one of the more quietly remarkable engineering solutions of early Ireland. Where stone roads demanded quarrying and labour, a togher demanded a very different kind of skill: the ability to read a landscape, harvest the right timber, and weave a stable surface from what the surrounding woodland could provide.

The Derrynagran togher runs on an east-west orientation and measures just under four metres wide and half a metre deep, dimensions that suggest something built to last rather than improvised in a hurry. Its construction follows a logical layered system. A base of transverse and longitudinal ash roundwood, the thicker structural timbers reaching up to about eleven centimetres in diameter, provided the load-bearing frame. On top of this, builders laid a compact mat of longitudinal brushwood, principally ash and birch, each piece only two to two-and-a-half centimetres across, packed five or six layers deep. The result was a surface with enough give to absorb movement in the bog beneath while remaining firm enough underfoot. Ash and birch were not chosen at random; both are relatively fast-growing, workable, and resilient, and their presence here reflects a practical knowledge of local timber resources. The bog itself, by sealing the structure in anaerobic, waterlogged conditions, did what no deliberate preservation effort could have managed, holding the wood in a state that allowed its details to be recorded centuries or millennia after it was last walked upon.