Viking raid warfare and tactics
Vikings were members of tribes, originally from Scandinavia, of Norse ancestry, who gained a reputation for their raids and piracy in many parts of Europe, especially England, Ireland, and Frankish territories. The term "Viking Age" refers to the period roughly from 793 AD to the late 11th century in Europe. In this era Viking activity started with raids on Christian lands in England and eventually expanded to mainland Europe, including parts of present-day Russia. While maritime battles were rare, Viking bands proved very successful in raiding coastal towns and monasteries due to their efficient warships, and intimidating war tactics, skillful hand-to-hand combat, and fearlessness. What started as Viking raids on small towns transformed into the establishment of important agricultural spaces and commercial trading-hubs across Europe through rudimentary colonization. Vikings' tactics in warfare gave them an enormous advantage in successfully raiding (and later colonizing), despite their small population in comparison to that of their enemies.
Viking expansion
Our knowledge of Vikings in Iberia is mainly based on written accounts, many of which are much later than the events they purport to describe, and often also ambiguous about the origins or ethnicity of the raiders they mention. A little possible archaeological evidence has come to light, but research in this area is ongoing. Viking activity in the Iberian peninsula seems to have begun around the mid-ninth century as an extension of their raids on and establishment of bases in Frankia in the earlier ninth century, but although Vikings may have over-wintered there, there is as yet no evidence for trading or settlement.