Vikings in Iberia
The first incursion of the Vikings in Iberia has been characterised as 'probably the most significant episode of the whole period of Viking activity in the South'. It is mentioned in "Annales Bertiniani", and dated August 844, when a group from a plundering expedition entered the Garonne and reached Galicia. Despite storm damage, some proceeded to South-West Spain. This account is consistent with several later, but independent sources in Latin and Arabic. In particular, the late ninth- or early tenth-century "Chronicle of Alfonso III" adds that after plundering a number of coastal villages they were ultimately repulsed in the vicinity of "Farum Brecantium" (i.e. the Tower of Hercules). Ramiro I of Asturias gathered troops in Galicia and Asturia for the counter-attack. After the Asturian victory, the Vikings continued their voyage in direction of Lisbon. While some authors consider that the reliability of this chronicle is open to doubt, others consider that other local chronicles confirm the arrival of the Norsemen.
Kingdom of Dublin
Vikings invaded the territory around Dublin in the 9th century, establishing the Norse Kingdom of Dublin, the earliest and longest-lasting Norse kingdom in Ireland. Its territory corresponded to most of present-day County Dublin. The Norse referred to the kingdom as "Dyflin", which is derived . The first reference to the Vikings comes from the "Annals of Ulster" and the first entry for 841 CE reads: "Pagans still on Lough Neagh". It is from this date onward that historians get references to ship fortresses or longphorts being established in Ireland. It may be safe to assume that the Vikings first over-wintered in 840–841 CE. The actual location of the longphort of Dublin is still a hotly debated issue. Norse rulers of Dublin were often co-kings, and occasionally also Kings of Jórvík in what is now Yorkshire. Under their rule, Dublin became the biggest slave port in Western Europe.