The one at Killeen in County Mayo is a rath, the term used for a ringfort constructed from earthen banks rather than stone, typically enclosing a circular area that once served as a defended farmstead during the early medieval period, roughly between the fifth and twelfth centuries. These were not military fortifications in any grand sense, but the fortified homesteads of farmers and minor lords, the banks and ditches serving to keep livestock in and wolves or rivals out.

The Killeen example sits within a Mayo landscape that has been continuously farmed and settled since prehistory, a county whose townlands preserve layer upon layer of occupation. The placename Killeen itself derives from the Irish "cillín", most commonly used to denote a small, unconsecrated burial ground, often used historically for unbaptised infants, though the name does not necessarily indicate one is present here. The rath would have been a focus of daily rural life for whoever enclosed it, and in Irish tradition such sites accumulated a considerable folklore weight over the centuries, frequently associated with the fairies or "sí", which helped ensure many survived simply because local people were reluctant to disturb them.