That proximity is unlikely to be accidental. Magh Adhair was the traditional inauguration place of the Dál Cais, the dynasty from which Brian Boru emerged, and the broader natural amphitheatre formed by the landscape here, along the east bank of the Hell River, appears to have concentrated several related monuments within a relatively compact area.

The rath itself, a ringfort of the kind once scattered across Ireland in their thousands, takes the form most commonly associated with early medieval settlement and landholding, roughly between the sixth and tenth centuries. A rath is defined by an earthen bank enclosing a roughly circular interior, often with a ditch, or fosse, outside the bank to add both drainage and defensive depth. This example at Toonagh is modest in scale, measuring about 21.8 metres north to south and 20.6 metres east to west across the interior. Its earthen bank survives to an external height of between 0.7 and 1.6 metres, reducing to a scarp on the western side. Beyond that runs a fosse, still 0.4 to 0.8 metres deep, and an outer bank that continues from the east around through the south to the west. Two entrances, each about 4 metres wide, are cut through the inner bank, one facing east and one to the north-north-west. A further enclosure adjoins it to the north-east, suggesting that whatever activity took place here, it extended beyond a single enclosed space.

The cluster of monuments gathered within this natural bowl of land, the ceremonial mound, the adjoining enclosure, and this rath positioned at the amphitheatre's north-western edge, gives the site a layered quality that its modest earthworks alone would not suggest.