Brian Boru in the context of "History of Ireland (800–1169)"

The Battle of Clontarf (Irish: Cath Chluain Tarbh) took place on 23 April 1014 at Clontarf, near Dublin, on the east coast of Ireland. It pitted an army led by Brian Boru, High King of Ireland, against a Norse-Irish alliance comprising the forces of Sigtrygg Silkbeard, King of Dublin; Máel Mórda mac Murchada, King of Leinster; and a Viking army from abroad led by Sigurd of Orkney and Brodir of Mann. It lasted from sunrise to sunset, and ended in a rout of the Viking and Leinster armies.

It is estimated that between 7,000 and 10,000 men were killed in the battle, including most of the leaders. Although Brian's forces were victorious, Brian himself was killed, as were his son Murchad and his grandson Toirdelbach. Leinster king Máel Mórda and Viking leaders Sigurd and Brodir were also slain. After the battle, the power of the Vikings and the Kingdom of Dublin was largely broken.

The Cycles of the Kings or Kings' Cycles, sometimes called the Historical Cycle, are a body of Old and Middle Irish literature. They comprise legends about historical and semi-historical kings of Ireland (such as Buile Shuibhne, "The Madness of King Suibhne"), stories about the origins of dynasties and peoples (such as The Expulsion of the Déisi), accounts of significant battles (such as Battle of Mag Mucrama), as well as anecdotes that explain rites and customs. It is one of the four main groupings of early Irish sagas, along with the Mythological Cycle, the Ulster Cycle and the Fianna Cycle.

The kings that are included range from the almost entirely fictional Labraid Loingsech, who allegedly became High King in the 4th century BC, to the entirely historical Brian Boru. Other kings include Cormac mac Airt, Niall of the Nine Hostages, Conall Corc, Diarmait mac Cerbaill, Lugaid mac Con, Conn of the Hundred Battles, Lóegaire mac Néill and Crimthann mac Fidaig. It was part of the duty of the medieval Irish bards, or court poets, to record the history of the family and the genealogy of the king they served. This they did in poems that blended the mythological and the historical to a greater or lesser degree.