21 April 1006
1006 was the year in which Brian Boru completed his circuit of Ireland, a feat attempted but held up two years earlier. Ireland was united by Boru in 1002, regarded as significant moment in Irish unification. The time between 1002 and 1014 was a period of unity. Brian was born Brian Mac Cennétig and later called himself Brian Boru - 'of the tributes' (after the unification of Ireland) as he collected tributes from all the clan kings of the time, using the money to restore monasteries and libraries.
Sources: http://www.homeatfirst.com/brianbor.htm and
http://www.ireland-information.com/articles/brianboru.htm

Easter was a time of significance for Boru, and Ireland in later centuries. At Easter 1014 Brian won a battle against the Norse but lost his own life, mortally wounded by a retreating commander. The Easter uprising of 1916 began on Easter Monday; while the Good Friday peace accord (the beginning of the end of hostilities) was announced at 5.36pm on Good Friday, 10 April 1998.

The following account of Brian Boru is given by the Clare County Library:

Brian Boru was born around 940, the youngest of two sons of Cennedig, head of Dal Cais, one of the royal free tribes of Munster. Brian grew up during the worst days of tyranny when the Dalcassians had been driven in to the present county of Clare. Brian’s brother, Mahon, being the eldest, succeeded Cennedig as chief of the Dalcassians. Being hemmed into Clare by the Norse Leader, Ivar of Limerick, Mahon was willing to accept terms but Brian, seeing almost all of the Dal Cais tribe including his mother brutally murdered by a Norse raid when he was only a child, refused to be any part of such a truce. He deserted Mahon with a group of soldiers. They lived in the hills of Munster attacking Norse settlements and disappearing in to the hills. His fame spread throughout the province and infuriated Ivar. Although having only a handful of men, Brian’s skill as a tactician led him to defeat vastly superior numerical forces and led to rumours of a mighty Dalcassian army.

After a number of petty battles, Brian had trained an excellent Dalcassian army to face the Norsemen. The stories of his triumphs had led to vast numbers of young men volunteering to join his side. The feud between himself and Mahon ended. Mahon renounced his truce with the Norsemen and the two brothers rejoined forces. The two men triumphed so far that Mahon took the throne of Cashel in 963 and in 968 at Sulchoid in Tipperary, the two brothers completely overtook Ivar’s forces and marched on Limerick while Ivar fled back to the Norse lands. The Norse tyranny in Munster thus collapsed and Mahon ruled peacefully for eight years. However, Ivar returned to Ireland and plotted the murder of Mahon. After Mahon’s death, Brian not wanting a bloodbath between his forces and Ivar’s, honourably challenged Ivar to open combat, which he won killing Ivar. Brian succeeded his brother as head of the Dal Cais and immediately took the field against his brothers enemies. In 978, he defeated the King of Cashel in battle. Step by step he established himself in the Kingship of Munster and fortified the province. In 983 and 988, his fleets ravaged Connaught and plundered Meath.

Meanwhile, another great leader had arisen in the North, Malachy the second, the Ui Neill King of Tara. Malachy was born in 948, became King of Meath and in 980, High King. This he achieved at the battle of Tara in 980 where he overthrew a Norse Army and took Dublin. A clash between the two men was inevitable. At last, in 998, they met and divided Ireland between the two of them, Brian becoming the King of the South and Malachy of the North.

By 1002, the joint sway of Malachy and Brian could not last. Malachy, being unable to gather enough support to take on the mighty forces of Brian, allowed Brian peacefully to take over his lands. This was the greatest moment in the history of native Ireland. Brian, by his title, “Ard Ri”, was claiming the monarchy of the whole Gaelic race. Before Brian, and Malachy, Ireland was divided in to a number of petty kingdoms, sometimes at peace, sometimes at war with one another. The Vikings themselves joined in the struggles between the Irish kingdoms and also fought bitterly among themselves. There was no one king up to this who was responsible for the defence of Ireland against the Vikings and had control over the entire island.

Brian had much to do as High King to lift Ireland out of the ruins of the Norse Age. He rebuilt ruined churches, built others, he sent overseas to replace lost books and artefacts and all that he possibly could to heal the wounds of the past two centuries of Norse pillage.

In 1013, the Leinstermen and the Dublin Vikings revolted against Brian. Mael Morda, King of Leinster, allied himself with the Dublin Vikings and went to war with Brian. The Dublin Vikings sought allies overseas. The great sigurd, Earl of Orkney, came with a large contingent. While other Viking contingents came from as far afield as Iceland and Normandy. Brian gave them Battle at Clontarf on Good Friday, 1014 and defeated them. However, as the Vikings were retreating, one of their leaders, Bothair, murdered Brian.

Source: http://www.clarelibrary.ie/eolas/coclare/people/brianbor.htm

See also the CELT The Annals of Ulster, an extraordinary resource for early Irish history:
http://www.ucc.ie/celt/published/T100001A/index.html