Medieval and early modern Irish literature portrays an almost unbroken sequence of High Kings, ruling from the Hill of Tara over a hierarchy of lesser kings, stretching back thousands of years. Modern historians believe this scheme is artificial, constructed in the 8th century from the various genealogical traditions of politically powerful groups, and intended to justify the current status of those groups by projecting it back into the remote past.
The concept of national kingship is first articulated in the 7th century, but only became a political reality in the Viking Age, and even then not a consistent one. While the High Kings' degree of control varied, Ireland was never ruled by them as a politically unified state, as the High King was conceived of as an overlord exercising suzerainty over, and receiving tribute from, the independent kingdoms beneath him.
Early Irish kingship was sacred in character. In the early narrative literature a king is a king because he marries the sovereignty goddess, is free from blemish, enforces symbolic buada (prerogatives) and avoids symbolic geasa (taboos).
According to 7th and 8th century law tracts, a hierarchy of kingship and clientship progressed from the rí tuaithe (king of a single petty kingdom) through the ruiri (a rí who was overking of several petty kingdoms) to a rí ruirech (a rí who was a provincial overking). (See Rí.)
Each king ruled directly only within the bounds of his own petty kingdom and was responsible for ensuring good government by exercising fír flaithemon (rulers' truth). His responsibilities included convening its óenach (popular assembly), collecting taxes, building public works, external relations, defence, emergency legislation, law enforcement, and promulgating legal judgment.