Modern research indicates Saint Cianán and his followers may have been the origin behind the tribal name as it is a late construction similar in form to Eóganachta and Connachta.
[1] The Ciannachta claimed descend from Tadc mac Céin, a member of "the possibly legendary early Munster dynasty, who was said to be a grandson of Ailill Aulom.
They are first recorded sub anno 535 when they were defeated in battle at Luachair Mór (between the rivers Nanny and Boyne), near Duleek, by Túathal Máelgarb.
A devastating seaborne attack by Ecgfrith of Northumbria in June 684,[5] which resulted in the seizing of a large number of slaves and the sacking of many churches and monasteries in Brega, was followed in 688 by the battle of Imblech Pich (Emlach, near Kells) an important defeat, inflicted upon them by King Niall mac Cernaigh, king of Brega.
After this, they lost their independence south of the Boyne and north of the Nanny Water, and from this point on were referred to as Ard Ciannachta, reflecting their loss of territory in south-east Brega.
These were located at the western end of Bellewstown ridge to the south of Duleek[9] close to the famous Lia Ailbhe, the standing stone described as 'the chief monument of Brega' (príomh-dindgnai Maighi Bregh) in 999, when it fell and was made into four millstones by Máelaschlainn the high king".
The political eclipse of Ciannachta Breg from mid-8th century onwards may have resulted in members of that dynasty transferring their ambitions to the ecclesiastical sphere where one of their kindred, Conmael ua Loichene, took the abbacy of the same church [ Monasterboice ] in 733.
The original can only have been the Connachta, whose power, position and prestige in the earliest part of the historical period are unquestionable and who loom large in prehistory as the traditional enemies of the Ulaid.