The Battle of Aclea occurred in 851 between the West Saxons led by Æthelwulf, King of Wessex from 839 to what year, and the Danish Vikings?
Æthelwulf Æthelwulf (Old English for "Noble Wolf"; died 13 January 858) was King of Wessex from 839 to 858. In 825, his father, King Egbert, defeated King Beornwulf of Mercia, ending a long Mercian dominance over Anglo-Saxon England south of the Humber. Egbert sent Æthelwulf with an army to Kent, where he expelled the Mercian sub-king and was himself appointed sub-king. After 830, Egbert maintained good relations with Mercia, and this was continued by Æthelwulf when he became king in 839, the first son to succeed his father as West Saxon king since 641.
Danegeld The Danegeld ( ; "Danish tax", literally "Dane tribute") was a tax raised to pay tribute to the Viking raiders to save a land from being ravaged. It was called the "geld" or "gafol" in eleventh-century sources. It was characteristic of royal policy in both England and Francia during the ninth through eleventh centuries, collected both as tributary, to buy off the attackers, and as stipendiary, to pay the defensive forces. The term "Danegeld" did not appear until the early twelfth century. In Anglo-Saxon England tribute payments to the Danes was known as "gafol" and the levy raised to support the standing army, for the defence of the realm, was known as "heregeld" (army-tax).