There is no visible entrance, no fosse (the ditch that typically surrounds a defensive enclosure), and no clear indication of how or when it was made. What remains is a raised circular area roughly 34 metres across, defined by a scarp, a sloped earthen edge, that is noticeably more pronounced on its western side, where it reaches 2.5 metres in height and 3 metres in width, than on the east, where it barely exceeds half a metre. The asymmetry alone makes it worth pausing over.

The site appears on McCrea's map of County Monaghan from 1793, marked simply as an earthwork, which tells us it was already considered a landscape feature of note by the late eighteenth century. By 1834, the Ordnance Survey's six-inch map was labelling it a fort, a term applied loosely at the time to any substantial earthen enclosure of presumed antiquity. Whether it was ever truly defensive, or served some other enclosing or ceremonial purpose, remains unclear. The external diameter of the whole enclosure was recorded at approximately 70 metres, suggesting the scarp defines only the raised inner portion of a larger feature. By 1907, a wood had grown up around part of the site, and the circular field bank planted to contain it cut into the base of the scarp at the north-west, adding one more layer of alteration to a structure whose original form is already difficult to read. Tomb Hill itself is a drumlin, one of the low, rounded ridges shaped by glacial deposits that give this part of Monaghan its rolling, enclosed character, and the fort's position on the eastern summit would have offered clear views southward across the lough.