Nia Segamain, son of
Adamair, was, according to medieval Irish legend and historical tradition, a
High King of Ireland. He took power after killing his predecessor,
Conall Collamrach.
Geoffrey Keating says his mother was the presumed woodland goddess
Flidais of the
Tuatha Dé Danann, whose magic made wild
does give milk as freely as domesticated cattle during his reign. He ruled for seven years, until he was killed by
Énna Aignech. The
Lebor Gabála synchronises his reign with that of
Ptolemy VIII Physcon in
Egypt (145–116 BC). The chronology of Keating's
Foras Feasa ar Éirinn dates his reign to 226–219 BC, that of the
Annals of the Four Masters to 320–313 BC. His name means "sister's son or champion of Segamon", and is perhaps related to
Segomo, an ancient
Gaulish deity equated in Roman times with
Mars and
Hercules. A slightly more historical Nia Segamain occurs in early
Eóganachta pedigrees, and this is sometimes interpreted as evidence for the Gaulish origins of the dynasties.