A rath, sometimes called a ringfort, is an enclosed farmstead of the early medieval period, typically defined by one or more earthen banks and ditches and used as a dwelling place for a farming family. The one at Rathduff in the townland of Ballyscanlan has been levelled, but it has not entirely disappeared. A broad, low scarp still traces the ghost of a roughly circular enclosure, measuring approximately 25 metres north to south and 22 metres east to west, sitting on a slight rise in otherwise level pasture with rolling ground beyond.

The site was already named on Ordnance Survey six-inch maps as early as 1838, and the name recurs on the 1922 edition, which suggests the local memory of what stood here persisted even as the earthwork itself was being worn away. The name Rathduff combines the Irish words for fort and black or dark, a common enough pairing in Irish placenames that may refer to the colour of the soil, the vegetation, or simply the character of the place as local people understood it. The River Deel runs roughly 250 metres to the south-east, marking the southern boundary of the townland, and the proximity of water to a rath is unremarkable; early medieval farmers chose their ground carefully, and a reliable water source nearby was a practical necessity rather than an incidental feature.