This is one of the few hints we get about early Irish kingship eligibility: that the High King must be without blemish.How one could be eligible for kingship seems to follow the system of tanistry. The Tanist is the second-in-command or second-in-line after a ruler, and not necessarily a descendant. Historically, the males of the clan would choose their next leader from among all the righdamhna ("kingly material"), which could include sons of the departed ruler.
This method persisted in Ireland until the early 17th century when English common law replaced it. In Ireland today, the echo of tanistry can be heard in the title of the deputy prime minister, Tánaiste.
The illustration shows the numerous kingdoms of Ireland, with each having its own king, although often neighboring kingdoms banded together for protection from larger alliances. Political marriages between kingdoms also contributed to descendants with legitimate claims to multiple kingdoms, which could help them unite under one ruler.
Irish kings had a different set of responsibilities than other European kings. For one, they did not have the authority to create laws. The laws were worked out by the Brehons, the judges/arbitrators who wrote tracts on what was right and proper for a working society. The kings' job was to support the law, not make it up. During times of emergency a king could create a law, but this was seen as only temporary.
The king was never above the law. He was not always directly subjected to restitution, however: a designated underling would have to suffer the consequences, and would then be compensated monetarily by the king. The king could lose his status, however, if he engaged in "non-kingly" activities such as being seen doing the work of a commoner, acting cowardly in battle, or traveling without a proper retinue.
Although limited in power when it came to the law, kings could collaborate with the church in developing laws. Adomnán of Iona produced a set of laws, the Cáin Adomnáin ("Law of Innocents"), which has the names of several kings attached to it showing heir involvement and support.
