Mac Cairthinn mac Coelboth of the Uí Enechglaiss, King of Leinster, died 446. Mac Cairthinn is one of the very earliest verifiable Irish kings. Though not listed in any extant Irish genealogies, the Annals of Innisfallen record his death at the battle of Mag Femen in the kingdom of Brega in 446. Almost uniquely, this otherwise unverifiable reference is coroboratted by an Ogham inscription on a stone near Slane in the neighbouring County Louth. Wikipedia
The definitive Wikipedia entry for Mac Cairthinn Mac Coelboth. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Mac_Cairthinn_mac_Coelboth