The site gives its name to the townland of Lislarheenmore, and that name, meaning something close to "fort of the little grey place" in its Gaelic roots, was considered significant enough to be hachured and labelled on Ordnance Survey maps as far back as 1842, and again on the 1916 edition. That kind of cartographic attention is not nothing. It suggests the feature was legible and locally meaningful long after the period in which it was built.

The structure itself is a rath, the most common form of Irish ringfort, typically used as a defended farmstead during the early medieval period, roughly between the fifth and twelfth centuries. This example measures approximately 37.5 metres on its northeast to southwest axis and 34.4 metres northwest to southeast, making it a modest but coherent example of the type. Its enclosing element varies in construction: a proper earth and stone bank along the southwest, between three and four metres wide and about 0.7 metres high on the interior face, gives way elsewhere to a simple scarp, or cut slope, rising between 0.8 and 1.2 metres. A fosse, the technical term for the ditch that typically runs outside a rath's bank, encircles the entire structure and is visible today partly because rushes have colonised the wetter ground within it, the kind of botanical clue that often marks old earthwork features across Ireland. The rath sits within a multiperiod field system, meaning the surrounding landscape carries its own separate and overlapping history of agricultural use that predates and postdates the fort itself.

Two gaps in the enclosing earthwork, one to the northeast and one to the southeast, present a small puzzle. They may be original entrances, placed to face specific compass points or to serve routes across the ridge. Equally, they may be nothing more than cattle gaps pushed through by farmers in more recent centuries. The ambiguity is part of what makes the site worth considering carefully, even from a distance.