The one at Aghanahil in County Galway has three. That alone sets it apart. Sitting in level grassland, this slightly oval earthwork measures roughly 41.5 metres east to west and 37.5 metres north to south, and its multiple lines of defence give it a heft and complexity unusual among surviving examples of its type.

A rath, to use the Irish term, was typically a defended homestead of the early medieval period, its enclosing bank and external ditch serving to define status and territory as much as to repel attack. At Aghanahil, the arrangement is more elaborate than most. Three banks survive, separated by two intervening fosses, the term used for the ditches cut between earthwork banks. Where the inner enclosing element has worn or shifted over the centuries, a scarp, a steep natural or cut slope, takes its place. The outermost bank, the most exposed to time and agriculture, remains visible along the north-east and south-west arcs of the circuit. That any of this survives in reasonably good condition, on what is now working farmland, is itself quietly remarkable.