Describe Viking raiding practices. How did the Carolingians respond to Viking invasions into their territory? How did Alfred in England respond?

After finally subduing the Saracen threat from the east, the eighth century brought to Europe a new invader--this time, unexpectedly from the north. These Scandinavians seemed but harmless savages conducting minor raids in the beginning, but they would soon wreak havoc throughout the Carolingian civilization. Although the main cause of their first attacks on western Europe are not known, from the start of the ninth century these Viking raids were already spreading so quickly that …

…longer be pacified by a mere ransom. It was this assault that led to the adaptation of the fortresses used by Alfred and Charles (the Bald) and to the eventual defeat of the Viking Great Army. However, it also changed the face of how battle would be fought throughout Europe in the following years, as burhs became motte and bailey 'castles,' and evolved into the famous stone castles Europe is so famous for today.