A drumlin is one of those smooth, oval hills left behind by retreating glaciers, and this particular one in Greaghfarnagh carries on its flank the remains of what is recorded as a fort, though the structure has been so altered by later use that even its entrance can no longer be identified.

The earthwork measures roughly 26 metres across internally, defined by an overgrown bank that varies considerably depending on where you take your measurements. At the north-east, the bank is just over three metres wide, rising about a metre on the exterior but barely a quarter of a metre on the interior side. By the time it reaches the north-west, it has been reduced to a simple scarp nearly two metres high. Between the inner bank and an outer one runs a fosse, the term for a defensive ditch, here about two and a half metres across at the top and less than half a metre deep at the north-east. The outer bank itself is modest, only a metre wide and twenty centimetres high, and it has been further complicated by a stone field wall built directly on top of it, suggesting that at some point a farmer simply incorporated the ancient boundary into their own land divisions. There are many gaps around the perimeter, and whether these represent collapsed sections, deliberate later breaches, or original features is now impossible to say with certainty. Michael J. Moore's Archaeological Inventory of County Leitrim, published in 2003, provides the detailed measurements that make it possible to describe the site at all, even in its compromised state.

What the site illustrates, perhaps more than anything, is how completely an early enclosure can be absorbed into an ordinary farming landscape. The stone wall riding the outer bank is a small but telling detail: not destruction exactly, but a kind of quiet overwriting, one boundary repurposed to serve another era's needs entirely.