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.
Viking expansion
The Vikings pillaged monasteries on Ireland's west coast in 795, and then spread out to cover the rest of the coastline. The north and east of the island were most affected. During the first 40 years, the raids were conducted by small, mobile Viking groups. From 830 on, the groups consisted of large fleets of Viking ships. From 840, the Vikings began establishing permanent bases at the coasts. Dublin was the most significant settlement in the long term. The Irish became accustomed to the Viking presence and culture. In some cases they became allies and also intermarried.