Sírna Sáeglach ("the long-lived"), son of Dian mac Demal, son of
Demal mac Rothechtaid, son of
Rothechtaid mac Main, was, according to medieval Irish legend and historical tradition, a
High King of Ireland. He separated the province of
Ulster from the authority of the High King, and is said to have made war against the
Ulaid, who had killed his great grandfather, for a hundred years according to the
Lebor Gabála Érenn, 150 years according to the
Annals of the Four Masters, but
Geoffrey Keating, citing an ancient poem, gives him only twenty-one years. According to one version of the
Lebor Gabála, the Ulaid united with the
Fomorians and gave him battle at Móin Trógaide in
County Meath, but a plague fell on them and the leaders of both sides died. According to another version, agreed by Keating and the Four Masters, Sírna was killed by
Rothechtaid Rotha at Alind. The
Lebor Gabála synchronises the start of his reign with the reign of
Deioces of the
Medes (694–665 BC), and his death with his successor
Phraortes (665–633 BC). The chronology of Keating's
Foras Feasa ar Éirinn dates his reign to 814–794 BC, that of the
Annals of the Four Masters to 1181–1031 BC. His Son was
Ailill Olcháin.