Upon the accession of a new monarch, he ascended the Sacred Stone, preserved inviolate for such occasions, and was inaugurated in the presence of the clergy and the laity by the principal bishop of the nation. Originally it is probable that the Druids were the necessary assistants on such occasions, their prerogatives passing to the clergy; for Columba is said by his biographer, Adamnan, to have “ordained” Aidan king of the Dalriads, an expression which cannot mean that Aidan’s title to the royal dignity was based upon the authority of the Abbot of Iona, but rather that the sanction of the sacerdotal order, which appears to have been considered indispensable to all political authority amongst the Celtic people from time immemorial, had been transferred upon the fall of the old religion, from the Druidical to the Christian priesthood.[35] Close to the _Ardrigh_, with his right foot planted on the same stone of honour, stood the _Righdomna_ or _Tanist_, the heir-apparent of the monarchy, who seems to have been nominated on the same occasion in pursuance of the true Celtic principle of “a divided authority,” the office being immediately filled up, in case of the premature death of the _Tanist_ during the lifetime of the reigning sovereign--a fatality of very frequent occurrence--the same rule being as applicable to the chieftain of the smallest territory as to the chosen leader of the nation. The power of the _Ardrigh_ over the provincial kings must have depended upon his ability to enforce it, and to exact the hostages which were invariably necessary to secure the obedience of the subordinate princes. _Can_ and _Cuairt_, or tribute and visitation, were amongst his rightful dues; in other words, in addition to the payment of a stipulated tribute, the _Oirrighs_ were bound to entertain the _Ardrigh_ and his followers in his annual progresses for a certain stated period in every year; a burdensome system of free-quarters by no means peculiar to the Celtic people, which could be exacted by every petty chieftain from the occupants of all the territory over which his influence extended.[36] The authority of the early Pictish kings over the various provinces of the confederacy was probably identical with that of the Irish _Ardrigh_ over the subordinate principalities of _Leth Cuin_ and _Leth Mogh_, and may be compared to the dominion exercised by Kent, Wessex, or Mercia, over the remaining South Humbrian kingdoms, at a time when either state was liable to exchange the situation of a ruling power for a subordinate and comparatively dependent position.[37]