Medieval Irish historical tradition held that Ireland had a High King (Ard Rí) based at Tara since ancient times, and compilations like the 11th-century Lebor Gabála Érenn, followed by Early Modern works like the Annals of the Four Masters and Foras Feasa ar Éirinn, purported to trace the line of High Kings. John T. Koch explains: "Although the kingship of Tara was a special kingship whose occupants had aspirations towards supremacy among the kings of Ireland, in political terms it is unlikely that any king had sufficient authority to dominate the whole island before the 9th century". Máel Sechnaill I is often considered the first historical High King, although he faced some opposition. Applying the title to earlier kings is considered anachronistic, while kings from before the 5th century are generally considered legendary. The traditional list of High Kings is thus a mixture of historical facts and legend.
The annals describe some later High Kings as rígh Érenn co fressabra ("Kings of Ireland with opposition"), which is a reference to the instability of the kingship of Tara from the death of Máel Sechnaill mac Domnaill in 1022. He had been overthrown by Brian Boru in 1002, and restored in 1014 following Brian's death, but Brian's example was followed by many other dynasties in the century following 1022. The High Kingship was effectively ended in the 1170s after the Anglo-Norman invasion, its last holder being Ruaidrí Ua Conchobair.
