The first Battle of Reading was a battle on 4 January 871 at Reading in what is now the English county of Berkshire. It was one of a series of battles, with honours to both sides, that took place following an invasion of the then kingdom of Wessex by an army of Danes led by Bagsecg and Halfdan Ragnarsson in an attempt to conquer Wessex. Both battle and campaign are described in the Anglo-Saxon Chronicle, and this account provides the earliest known written record of the existence of the town of Reading.
The Danes had established a camp at Reading, defended by the Thames and Kennet rivers on two sides, and by a rampart on the western side. Three days after their arrival, a party of Danes rode out towards nearby Englefield, where a West Saxon force under the command of Æthelwulf, the Ealdorman of the shire, was waiting for them. In the ensuing Battle of Englefield many of the Danes were killed, and the rest driven back to Reading.
Four days later, Æthelwulf had been joined by the main West Saxon army, led by King Æthelred and his brother, Alfred the Great. The entire Saxon force marched on Reading. The assault was directed mainly at a gateway through the ramparts, and fierce and bloody fighting followed, before the attack was repulsed. Among the many dead of both sides was Æthelwulf. The Saxon forces were forced to retreat, allowing the Danes to continue their advance into Wessex.
Following the Battle of Reading, Æthelred and Alfred reformed their army, and a few days later won a famous victory at the Battle of Ashdown, forcing the Danes to retreat to Reading once more. Two weeks later the Danes won the Battle of Basing, and then, on 22 March, the Battle of Marton. In April Æthelred died, to be succeeded by Alfred. The Danish army remained in Reading until late in 871, when they retreated to winter quarters in London, and much of King Alfred's 28-year reign was taken up with the Danish conflict.