The Three Collas

The Three Collas were, according to medieval Irish legend and historical tradition, the fourth-century sons of Eochaid Doimlén, son of Cairbre Lifechair. Their names were: Cairell Colla Uais; Muiredach Colla Fo Chrí (also spelt Colla Dá Crich, or Fochrich); and Áed Colla Menn. Colla Uais ruled as High King of Ireland for four years.

According to tradition, the Three Collas killed their uncle, Fíacha Sroiptine, at the Battle of Dubhchomar, in Crioch Rois, Breagh, with Colla Uais taking the kingship. It was prophesied that whoever killed them, his descendants would never rule Ireland. Colla Uais ruled in Fíacha's place for three years (323-326 AD), and as High-King of Ireland for four years, until Fiacha's son Muiredach Tirech banished the Three Collas, exiling them and three hundred followers to Alba (Scotland).

The mother of Three Collas was said to be Ailech, the daughter of Udhaire, king of Alba. According to Keating's version Udhaire put them in command of three hundred warriors. After that they returned to Ireland, hoping that Muiredach might kill them, and deprive his descendants of the throne. But Muiredach knew of the prophecy, and despite knowing they had killed his father, took them into his service.

After several years, Muiredach decided the Collas should have territory of their own, and sent them to conquer Ulster. With an army drawn from Connacht, they fought seven battles in a week against the Ulaid at Achaidh Leithdeircc, killing Fergus Foga, king of Ulster, in the seventh. Colla Menn also died in this battle. They burned Emain Macha, the Ulster capital, after which it was abandoned, and seized substantial territories in mid-Ulster, thought to be the origin of the kingdom of Airgíalla.

The chronology of Keating's Foras Feasa ar Éirinn dates Colla Uais' High Kingship to 306–310. The Annals of the Four Masters dates his High Kingship to 322–326, and his destruction of Emain Macha and conquest of Ulster to 331. However, the chronology of early Irish historical tradition is known to be artificial. One story makes Fiachra Cassán of the Airgíalla, son of Colla Fo Chrí, the foster-father of Cormac mac Airt, who according to the usual chronology was his own great great grandfather, and an alternative tradition dated the fall of Emain Macha to 450.

The sixth century female saint, Derchairthinn, associated with Oughter Ard near Straffan, County Kildare, was said to be "of the race of Colla Uais, Monarch of Érinn".

According to a theory advanced by T. F. O'Rahilly, the traditional story of the Three Collas is not historical, although it has a basis in history. O'Rahilly argues that the breaking of the power of the Ulaid, the destruction of Emain Macha and the establishment of the kingdoms of the Airgialla were actually accomplished by the three sons of Niall Noígiallach, Conall, Endae and Eógan, who established the kingdoms of Tir Eógan and Tir Conaill in north-western Ulster in the mid-5th century. He believes the Three Collas are literary doublets of the three sons of Niall, their story a genealogical fiction intended to give the tributary kingdoms of the Airgialla a noble pedigree. This theory is followed by more recent historians, including Francis J. Byrne, and Dáibhí Ó Cróinín.

Donald Schlegel claims the brothers' tripartite names to be the only examples in ancient Ireland of brothers using the Roman style naming convention of personal name followed by family name followed by an epithet. This may reflect their alleged "return" from exile in Alba, which at the traditional time of their story—the 4th-century—was part of the Roman Empire. Schlegel suggests that being put in command of 300 soldiers may have meant that were centurions in the Roman army.

Schlegel also argues that the Three Collas, along with their name "Colla", may have descended from the Trinovantes of Britain. He claims that Trinovantes mistranslated by Ollams into Irish could have produced the name Airgíalla, the name given to the territory the Three Collas conquered in Ulster. In regards to Colla, it may derive from the names Coill or Coel, both of which Geoffrey Keating mentioned in the area the Trinovantes lived, Camulodunum (modern-day Colchester).