The one at Kilderry in County Kerry is a rath, the term used for an earthen ringfort, typically a circular enclosure defined by one or more banks and ditches, built and occupied during the early medieval period, roughly between the fifth and twelfth centuries. These were the farmsteads of their age, home to a family and their livestock, and the sheer number that once existed suggests a landscape far more densely and deliberately organised than the open fields and boreens that replaced them.

Kilderry itself is a quiet townland in Kerry, a county where the density of early medieval settlement has left traces in almost every field corner. The word rath points to an earthen construction rather than a stone cashel, the latter being the more common form in the rocky west, where loose stone was easier to gather than soil could be heaped. A typical rath would have enclosed a timber house, perhaps a souterrain, an underground stone-lined passage used for storage or refuge, and space enough for animals to be brought in at night. The circular bank was less a military fortification than a statement of ownership and a practical barrier against wolves and cattle thieves.