This impressive earthwork was recorded in the OS Letters of 1839 simply as ‘a large moat’, whilst the historian Carrigan offered more colourful detail in 1905, noting it as ‘a fine rath on the brow of a sharp incline’. He also revealed its older name of Donore, from the Irish Dún-uabhair, meaning either ‘the Fort of pride’ or ‘the proudly-situated Fort’; both translations seem fitting given its commanding position above the valley.

The monument itself consists of a raised circular platform approximately 20 metres in diameter and rising 4 to 5 metres high, surrounded by a substantial fosse about 4 metres wide and 1.75 metres deep. Beyond this defensive ditch runs an outer bank, 5 metres wide and standing about a metre high on its exterior side, though it has degraded at the south and been levelled entirely on the southwest. The flat-topped platform shows signs of internal division, with the western half sitting slightly higher than the eastern, separated by a subtle scarp running north to south across the centre that rises between 30 and 50 centimetres.

Though heavily overgrown today, this ringfort represents a typical example of early medieval defensive architecture in Ireland. These circular earthworks, often called raths or ringforts, were constructed between roughly 500 and 1200 AD and served as fortified homesteads for farming families of various social standings. The substantial nature of Thornback Rath, with its impressive height and multiple defensive features, suggests it may have belonged to someone of considerable local importance.