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.
Ranulf I of Aquitaine Ranulf I (also "Ramnulf", "Rannulf", and "Ranulph") (820–866) was a Count of Poitiers (from 835) and Duke of Aquitaine (from 852). He is considered a possible son of Gerard, Count of Auvergne, and Hildegard (or Matilda) "[more likely Rotrude, see Gerard, Count of Auvergne and Louis the Pious]", daughter of Louis the Pious and Ermengard. Few details are known about Ranulf I, except that he died in 866 in Aquitaine from wounds received in the Battle of Brissarthe against the Vikings (in which Robert the Strong also died).