The monument at Portnashangan has been so thoroughly levelled that nothing is visible to anyone walking the site today, yet aerial photography taken in November 2011 revealed a circular crop mark approximately 22 metres across, the kind of ghostly outline that appears when buried features affect how soil retains moisture and nutrients, causing the vegetation above them to grow differently from the surrounding land.

The confusion around what this place actually was goes back at least to the nineteenth century. The 1837 Ordnance Survey Fair Plan map depicted it as an oval earthwork with a circular feature at its centre and labelled it simply as a fort, the catch-all term surveyors of that era frequently applied to any earthen enclosure of uncertain origin. Later analysis of the same OS mapping suggested the site was more likely a ring barrow, a type of prehistoric funerary monument in which a burial mound is enclosed by a circular bank and ditch, rather than a ringfort, which was a defended farmstead typically dating from the early medieval period. The distinction matters because it shifts the likely date of construction back considerably, from perhaps the first millennium AD into prehistory. Whether the original surveyors misread the earthwork or simply had no better category available to them, the label stuck long enough to cloud the record.