Battle of Reading: Æthelred of Wessex and his brother Alfred are defeated by a Danish invasion army.

The Battle of Reading was a victory for a Danish Viking army over a West Saxon force on or about 4 January 871 at Reading in Berkshire. The Vikings were led by Bagsecg and Halfdan Ragnarsson and the West Saxons by King Æthelred and his brother, the future King Alfred the Great. It was the second of a series of battles that took place following an invasion of Wessex by the Danish army in December 870.

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.

Alfred the Great was King of the West Saxons from 871 to 886, and King of the Anglo-Saxons from 886 until his death in 899. He was the youngest son of King Æthelwulf and his first wife Osburh, who both died when Alfred was young. Three of Alfred's brothers, Æthelbald, Æthelberht and Æthelred, reigned in turn before him. Under Alfred's rule, considerable administrative and military reforms were introduced, prompting lasting change in England.

January 4 is the fourth day of the year in the Gregorian calendar; 361 days remain until the end of the year.