A good number have two. The rath at Barnycarroll in County Mayo has three, each one nested around the next, creating a concentric series of earthen ramparts, ditches, and banks that speaks to an unusual level of effort, and possibly of anxiety, on the part of whoever built it. It sits on raised pasture ground with views in every direction, which is precisely the kind of position that rewards both vigilance and display.

A rath, broadly speaking, is a roughly circular enclosure defined by earthen banks and ditches, most commonly associated with early medieval settlement in Ireland, typically between the sixth and tenth centuries. What makes the Barnycarroll example particularly legible is how well preserved it remains. The innermost bank rises to an external height of around three metres on its southern side, and its flat top is wide enough to walk along. Large blocky stones protrude from the internal slope, the surviving traces of stone facing that once lined it. Beyond that inner bank lies a fosse, a ditch, then a middle bank, and beyond that a second fosse and an outermost bank, steep-sided and still used in places as a field boundary, with later field walls radiating outward from it. That outermost bank may not have been part of the original design; a six-metre section at the south-east has been rebuilt in stone at some point. The entrance, a gap of just under three metres cut through the inner bank at the east-south-east, opens onto a slightly sunken passageway that crosses the innermost ditch with its own flanking banks. A causeway hint survives across the second ditch, though the outermost bank shows no corresponding break. The interior is level and grassy, and beneath it lies a souterrain, an underground stone-lined passage or chamber of the kind frequently found within early medieval enclosures, used variously for storage or refuge. Its surface openings are visible in the south-west quadrant, west of centre, and in the inner bank on the west-south-west side. Hawthorn and gorse have colonised the western perimeter. What gives the site an additional quality is that it does not sit alone: another rath lies 235 metres to the north, and a further enclosure and rath are within 363 metres to the north-west, suggesting that this was once a settled, organised landscape rather than an isolated stronghold.