The one at Lismoran, in County Mayo, is a rath, the term used for an earthen ringfort, as distinct from its stone-built equivalent, the cashel. A rath typically consists of one or more circular earthen banks and ditches enclosing a domestic area, and was most commonly used as a defended farmstead during the early medieval period, roughly between the fifth and twelfth centuries.

The place name itself offers a quiet clue to the site's presence. "Lios" is the Irish word for a ringfort or enclosed area, and its survival in the modern townland name Lismoran suggests that this particular earthwork was significant enough, or visible enough, to shape how local people named the land around it. That kind of linguistic persistence is not unusual in Ireland, where early medieval settlement patterns left their mark on the map as well as the ground, but it does lend the site a certain continuity, the fort naming the land, and the land preserving the fort's memory long after its original inhabitants are forgotten.

Beyond its presence in the Mayo landscape and the echo of its name in the townland, the specific history of this rath remains undocumented in publicly available sources at present. What can be said is that Mayo contains a considerable concentration of early medieval settlement remains, and a rath in this part of Connacht would have sat within a landscape that was actively farmed and socially organised long before the arrival of Anglo-Norman influence in the later medieval period. The earthworks, whatever their current condition, are a physical remnant of that earlier, quieter world.