The mound at Magh Adhair is believed to be a ring-barrow, a type of circular prehistoric burial monument, that was reused centuries after its original construction as a place of royal ceremony. No scientific excavation of the site has ever taken place, so everything understood about it has been pieced together from its landscape position, its physical form, and the scattered references that survive in medieval annals and bardic texts.

The earliest written evidence for the site comes from the ninth century. The Annals of the Four Masters record that in AD 877, Flan Sunagh of Cashel invaded Thomond and, in an act of deliberate provocation, stopped at Magh Adhair to play chess. The gesture was clearly understood as an insult to the Dál gCais, the dynasty for whom this was an assembly site of considerable political weight. In AD 982, Máel Sechnaill, king of Temair, went further and cut down a sacred tree associated with the site, and another was felled in 1051 by Aedh O Conor, King of Connacht. The destruction of a sacred tree at an inauguration site was a recognised act of symbolic aggression, intended to strike at the ceremonial legitimacy of a ruling dynasty. By the thirteenth century, Magh Adhair had become the established inauguration place of the Uí Bhriain, the descendants of Brian Boru. The medieval text Caithréim Thoirdhealbhaigh records seven Uí Bhriain inaugurations between 1242 and 1313, with Mac Con Mara of Clann Chuileáin officiating at each one. In October 1598, it was reported that Tadhg was to be inaugurated as Ó Briain, a ceremony presumed to have taken place here. If so, it would have represented more than seven hundred years of royal elections at the same site, a prehistoric mound quietly absorbed into the political life of medieval Ireland and still in use as Tudor armies reshaped the country around it.