It is possible, that a Viking attack on the North Ireland coast and the Hebrides in 617 AD was the Vikings, but this cannot be proven. The first official attack on Ireland by the Vikings took place in 794 AD, about 10 years after the first attacks on the English coast, at Rechru (now the island of Lambay) very close to what is now Dublin. The raids continued for approximately 40 years, until finally in 832 AD the Vikings attacked in force under command of warrior named Tuirgeis. One thousand warriors were under the command of Tuirgeis, and they sailed up the Liffey and the Boyne rivers raiding the interior of Ireland and establishing forts. Another fort was established as a base for the Vikings in 837 AD at Ath Cliath, which was also, called Dubhlinn (Dublin).
Armagh, Irelands Holy City, and the home of the abbot were taken, and the abbot was evicted. Tuirgeis quickly turned the church into a pagan temple and made himself the high priest of the new religion. Most of North Ireland was now in the hands of Gaill (strangers). This was due in a large extent to the fact that there was not a powerful High King in Ireland at the time. The tribal Kings were bickering among themselves and frequently allied with the Norwegian Vikings to conquer an enemy. In 847, the tide turned for the Norwegian Vikings, as a new Viking force arrived. The Danish Vikings, who had successfully conquered Northumbria in England and Brittany in France now, arrived on the scene. They were well organized and had a much shorter line of supply. With these advantages the Danes (dark foreigners or heathen) quickly went to battle with the Norweigan Vikings (white foreigners or heathen) over control of Ireland. It was during the early tenth-century Viking attacks that monks took refuge in tall tapered round towers with conical caps. Built of stone and mortar with narrow doors raised at least ten feet from the ground, they were designed to withstand fire and attack, and to serve as belfries in times of peace. Complete towers can still be seen at Devenish and Antrim in Ulster, and Glendalough in Leinster, with others in various states of decay at Drumbo, Nendrum, Clones, Armoy, Drumlane, Tory Island and many other places.
The battles took place at Sciath-Nechtin, Dublin, and at Carlingord Lough with the Danes emerging the victors in approximately 850 AD. The Norwegians countered a few years later regained control of a majority of the land. This back and forth battle continued for many years, as the Vikings had taken on an attribute of the Irish, and were now fighting among themselves for control of the land. They frequently went to the Irish for help against their opponent while the Irish did the same in their wars with others of their kind.
In the early 10th Century, the Danes again largely took control of the land. But this was not to last for long. The Irish had learned much over the last century, they now knew how to build warships and understood sea tactics for battle. Their first victories were recorded by Cellachan of Cashel, who sacked the Viking capital of Dublin in 950 AD.
Brian put up with these few small remaining Viking strongholds, as he apparently considered them a means to forward trade with other nations. He even married in an attempt to strengthen relations with the remaining Danes in Ireland. But differences of opinion among family soon brought the matter to a head again. The Danes considered themselves insulted and requested reinforcements from all the Viking lands, which came without reluctance. Forces arrived from the Orkneys, Norway, France, Britain and Denmark in response to the request. In early 1014, sometime around Palm Sunday, the two sides met in battle. Both armies numbered around 20,000 men and met outside Dublin in the Battle of Clontarf. The Vikings wore mail armor, which should have been an advantage, but spread their lines too thin. In the end, the Irish under Brian Boru won the battle, but Brian himself was killed. Although Dublin remained a Danish outpost for years after the battle, Viking power was forever broken in Ireland.
Brian Boru (Brian mac Cennetig or Brian Boroimhe in Gaelic) was born in Munster, Ireland. A member of the Dal Cais (Delcassians) tribe, he was the brother of Mahon, who became King of Munster following the death of their father, Cenn-tig. His father was Cennétig mac Lorcáin, King of Thomond and his mother was Bé Binn ingen Murchada, daughter of the King of West Connacht. Annals of Munster
- Father: Cenn-tig (King of Thomond)
- Mother: Bé Binn ingen Murchada
- Brother: Mahon (King of Thomond)
- Wife: Mór Son: Murchad (d. 1014, at Battle of Clontarf with his father)
- Wife: Echrad
- Son: Tadc; Tadhg Ua Brian, rí Mumhan
- Wife: Gormflaith (daughter of Murchad MacFinn, King of Leinster), granddaughter of Finn macMáel Mórda O'Fáeláin
- Son: Donnchad
The origin of his cognomen Boru or Boruma (Tributes) is believed to relate to a crossing point on the river Shannon where a cattle-tribute was driven from his sept, the Dál gCais to the larger sept to which they owed allegiance, the Eóganachta. Later legends originated to suggest that it was because he collected monies from the minor rulers of Ireland and used these to rebuild monasteries and libraries that had been destroyed during Norsemen (Viking) invasions.
Mahon desired peace with the Vikings and attempted to attain it, but his younger brother Brian shared no such desire. In fact, after having witnessed the death of his mother and much of the Dal Cais tribe in a Norse raid while he was a child, Brian was a proponent of warfare with Vikings. When he was old enough, Boru broke away from his brother to wage guerrilla warfare on the Norse. A skilled tactician, he won many decisive victories that instilled fear in the enemy as well as their Irish allies. Boru's influence continued to grow throughout Southern Ireland and he became known for rebuilding many of the churches and other monuments that had been destroyed by the Norse.
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.