The site at Lisgorran is a rath, the term used for a roughly circular earthen enclosure built during the early medieval period in Ireland, typically as a defended farmstead. What makes this one quietly odd is that it has survived in the landscape long enough to appear on three separate maps spanning more than a century, yet its original entrance has never been positively identified, and the fosse, the defensive ditch that normally runs outside the bank of such enclosures, has left no visible trace at all.

The rath sits at the northern end of a ridge running roughly north-northeast to south-southwest, a classic position that would have offered both visibility and a degree of natural elevation. It measures approximately 43 metres east to west and 38 metres north to south, with a slightly domed interior. The enclosing earthen bank is best preserved at the north-northeast, where it stands 2.4 metres on the outside face, though only 0.7 metres on the interior, suggesting considerable build-up of soil over time. The bank's base is some 3.6 metres wide at that point. By the northwest and north, the hedge that once helped define the perimeter has almost entirely vanished. The rath was recorded on McCrea's Map of County Monaghan in 1793, and again on the six-inch Ordnance Survey maps of 1834 and 1907, meaning it was a recognised feature of the local landscape well before systematic archaeological survey began. Today, a farm track runs along the outside of the bank to the southwest, and old farm buildings cluster near the perimeter to the southeast and south, the working countryside having grown up quietly around a structure that predates it by well over a thousand years.