This is a rath, the commonest type of early medieval enclosure in Ireland, typically built between roughly the fifth and twelfth centuries as a farmstead for a single family or small community. What is easy to miss, standing on the ridge at Colgagh, is how much structural logic survives: the raised interior platform, the encircling bank, and, just beyond it, the fosse, a defensive ditch that once reinforced the whole arrangement.

The enclosure measures twenty-six metres in diameter, its bank of earth and stone now only about a third of a metre above the interior surface and roughly three and a half metres wide, worn down by time and livestock. The fosse outside it is similarly shallow, around thirty centimetres deep and just under four metres across, and has silted up considerably along its eastern arc. A three-metre gap in the bank on the eastern side marks the original entrance, and traces of a causeway across the fosse can still be made out at that point, indicating how residents would once have passed in and out. The north-east arc of the bank is the most damaged section; a now-disused quarry has removed part of it entirely. Smaller breaks in the bank at the south-west and north-west are the work of livestock rather than history, gaps worn through by animals moving across the ridge over generations.

The site is on working farmland, and the wet pasture means the ground can be soft underfoot. The causeway at the east entrance and the partially in-filled fosse on the south-eastern side are the details most worth seeking out, since they give the clearest sense of how the enclosure once functioned as a deliberate, designed threshold between the domestic interior and the world outside.