The Battle of Meretun (or Merton) between a West Saxon army led by King thelred and his brother, the future King Alfred the Great, and a Danish 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.

Æthelred I (alt. Aethelred, Ethelred; Old English: Æthel-ræd, lit. 'noble counsel'; 845/848 to 871) 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.

Æthelred's accession coincided with the arrival of the Viking Great Heathen Army in England. Over the next five years the Vikings conquered Northumbria and East Anglia, and at the end of 870 they launched a full-scale attack on Wessex. In early January 871, Æthelred was defeated at the Battle of Reading. Four days later, he scored a victory in the Battle of Ashdown, but this was followed by two defeats at Basing and Meretun. He died shortly after Easter. Alfred was forced to pay off the Vikings, but he scored a decisive victory over them seven years later at the Battle of Edington.

Æthelred's reign was important numismatically. Wessex and Mercia were close allies when he became king, and he carried the alliance further by adopting the Mercian Lunettes design, thus creating a unified coinage design for southern England for the first time. The common design foreshadowed the unification of England over the next sixty years and the reform coinage of King Edgar I a century later.