Æthelred of Wessex is defeated by a Danish invasion army at the Battle of Marton.

Æthelred I was King of Wessex from 865 until his death in 871. He was the fourth of five sons of King Æthelwulf of Wessex, four of whom in turn became king. Æthelred succeeded his elder brother Æthelberht and was followed by his youngest brother, Alfred the Great. Æthelred had two sons, Æthelhelm and Æthelwold, who were passed over for the kingship on their father's death because they were still infants. Alfred was succeeded by his son, Edward the Elder, and Æthelwold unsuccessfully disputed the throne with him.

The Great Heathen Army, also known as the Viking Great Army, was a coalition of Scandinavian warriors who invaded England in 865 AD. Since the late 8th century, the Vikings had been engaging in raids on centres of wealth, such as monasteries. The Great Heathen Army was much larger and aimed to conquer and occupy the four kingdoms of East Anglia, Northumbria, Mercia and Wessex.

The Battle of Meretun between a West Saxon army led by King Æthelred and his brother, the future King Alfred the Great, and a Viking army took place on 22 March 871 at an unknown location in Wessex, probably in one of the modern counties of Dorset, Hampshire, or Wiltshire.

March 22 is the 81st day of the year in the Gregorian calendar; 284 days remain until the end of the year.