First Viking age in Ireland

The first recorded Viking raid in Irish history occurred in 795 CE when Vikings, possibly from Norway, looted the island of Lambay. This raid was followed by attacks on the coast of Brega in 798 and the coast of Connacht in 807. These early Viking incursions, generally small and swift, interrupted the golden age of Christian Irish culture and heralded two centuries of intermittent warfare. The Vikings, primarily from western Norway, typically sailed via Shetland and Orkney before reaching Ireland. Among their targets were the Skellig Islands off the coast of County Kerry. These early raids were characterized by aristocratic free enterprise, with leaders like Saxolb in 837, Turges in 845, and Agonn in 847 noted in the Irish annals.

In 797, Áed Oirdnide of the Cenél nEógain branch of the Northern Uí Néill became King of Tara following the death of his father-in-law and political rival Donnchad Midi. His reign saw campaigns in Mide, Leinster, and Ulaid to assert his authority. Unlike his predecessor, Áed did not campaign in Munster. He is credited with preventing major Viking attacks on Ireland during his reign after 798, although the annals do not explicitly mention his involvement in conflicts with the Vikings.

The Viking raids on Ireland intensified from 821 onwards, with the Vikings establishing fortified encampments, or longports, such as Linn Dúachaill and Duiblinn (Dublin). Larger Viking forces began targeting major monastic towns, while smaller local churches often escaped their attention. One notable Viking leader, Thorgest, connected with attacks on Connacht, Mide, and Clonmacnoise in 844, was captured and drowned by Máel Sechnaill mac Maíl Ruanaid. However, the historicity of Thorgest is uncertain, and his depiction may be influenced by later anti-Viking sentiment.

In 848, Irish leaders Ólchobar mac Cináeda of Munster and Lorcán mac Cellaig of Leinster defeated a Norse army at Sciath Nechtain. Máel Sechnaill, now High King, also defeated another Norse army at Forrach the same year. These victories led to an embassy to the Frankish emperor Charles the Bald. In 853, Olaf, possibly a "son of the king of Lochlann," arrived in Ireland and assumed leadership of the Vikings, alongside his kinsman Ivar. Their descendants, the Uí Ímair, would remain influential for the next two centuries.

From the mid-9th century, Norse alliances with various Irish rulers became common. Cerball mac Dúnlainge of Osraige initially fought against Viking raiders but later allied with Olaf and Ivar against Máel Sechnaill, though these alliances were temporary. By the end of the 9th century, the Uí Néill high kings faced opposition from their kinsmen and the Norse of Dublin, highlighting the persistent internal divisions in Ireland.

Áed Findliath, succeeding Máel Sechnaill as high king, counted some successes against the Norse, notably burning their longports in the north in 866. His actions, however, may have hindered the economic development of the north by preventing the growth of port towns. The last mention of Olaf in the annals is in 871 when he and Ivar returned to Dublin from Alba. Ivar died in 873, described as "king of the Norsemen of all Ireland and Britain."

In 902, Irish forces expelled the Vikings from Dublin, although the Norse continued to influence Irish politics. A group of Vikings led by Hingamund settled in Wirral, England, after being forced out of Ireland, with evidence of an Irish presence in the region.

The Vikings exploited Ireland's political fragmentation to invade, but the decentralized nature of Irish governance made it difficult for them to maintain control. Despite initial setbacks, the Vikings' presence ultimately influenced Irish cultural activity, leading to the formation of an Irish scholarly diaspora in Europe. Irish scholars like John Scottus Eriugena and Sedulius Scottus became prominent in continental Europe, contributing to the spread of Irish culture and scholarship.