Four field banks converge on it from different directions, as though the modern agricultural world has been slowly negotiating with something older, unable quite to absorb it. The earthwork at Monyglen is a rath, the most common type of early medieval enclosure in Ireland, typically consisting of one or more circular or oval earthen banks enclosing a raised interior where a farmstead once stood. This one measures roughly 35 metres along its longer axis and sits on the south-east-facing spine of a small drumlin, the kind of low, rounded hill left behind by retreating glaciers that gives the Monaghan landscape its characteristic rumpled appearance.

What makes the Monyglen example quietly interesting is how legible it remains, despite centuries of agricultural pressure. The inner earthen bank is still distinct, separated from an outer bank by a fosse, which is simply a ditch or berm serving as a further line of definition. The outer bank itself has been largely absorbed into an existing field boundary, a common fate for such features and one that makes them easy to overlook unless you know what you are looking at. A narrow entrance, just 1.7 metres wide at the base, survives in the inner bank on the south-east side, which would have been the original point of access. The rath was recorded on McCrea's map of County Monaghan as far back as 1793, and appeared again on later editions of the Ordnance Survey six-inch maps, meaning it has been a recognised feature of this townland for at least two centuries of systematic cartography.