Vikings is the modern name given to seafaring people originally from Scandinavia (present-day Denmark, Norway and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded and settled throughout parts of Europe. They also voyaged as far as the Mediterranean, North Africa, Volga Bulgaria, the Middle East, and North America. In some of the countries they raided and settled in, this period is popularly known as the Viking Age, and the term "Viking" also commonly includes the inhabitants of the Scandinavian homelands as a collective whole. The Vikings had a profound impact on the early medieval history of Scandinavia, the British Isles, France, Estonia, and Kievan Rus'.Expert sailors and navigators aboard their characteristic longships, Vikings established Norse settlements and governments in the British Isles, the Faroe Islands, Iceland, Greenland, Normandy, and the Baltic coast, as well as along the Dnieper and Volga trade routes across modern-day Russia, Belarus, and Ukraine, where they were also known as Varangians. The Normans, Norse-Gaels, Rus' people, Faroese and Icelanders emerged from these Norse colonies. At one point, a group of Rus Vikings went so far south that, after briefly being bodyguards for the Byzantine emperor, attacked the Byzantine city of Constantinople. Vikings also voyaged to Iran and Arabia. They were the first Europeans to reach North America, briefly settling in Newfoundland (Vinland). While spreading Norse culture to foreign lands, they simultaneously brought home slaves, concubines and foreign cultural influences to Scandinavia, influencing the genetic and historical development of both. During the Viking Age, the Norse homelands were gradually consolidated from smaller kingdoms into three larger kingdoms: Denmark, Norway and Sweden.

The Vikings spoke Old Norse and made inscriptions in runes. For most of the period they followed the Old Norse religion, but later became Christians. The Vikings had their own laws, art and architecture. Most Vikings were also farmers, fishermen, craftsmen and traders. Popular conceptions of the Vikings often strongly differ from the complex, advanced civilisation of the Norsemen that emerges from archaeology and historical sources. A romanticised picture of Vikings as noble savages began to emerge in the 18th century; this developed and became widely propagated during the 19th-century Viking revival. Perceived views of the Vikings as violent, piratical heathens or as intrepid adventurers owe much to conflicting varieties of the modern Viking myth that had taken shape by the early 20th century. Current popular representations of the Vikings are typically based on cultural clichs and stereotypes, complicating modern appreciation of the Viking legacy. These representations are rarely accuratefor example, there is no evidence that they wore horned helmets, a costume element that first appeared in Wagnerian opera.

The Battle of Englefield was a West Saxon victory against a Danish Viking army on about 31 December 870 at Englefield, near Reading in Berkshire. It was the first of a series of battles that took place following an invasion of Wessex by the Danish army in December 870.By 870, the Vikings had conquered two of the four Anglo-Saxon kingdoms, Northumbria and East Anglia. At the end of 870 they launched an attempt to conquer Wessex and marched from East Anglia to Reading, arriving on about 28 December. Three days later they sent out a large party under two earls to forage and reconnoitre, and it was met at Englefield by an army of local levies under the command of Æthelwulf, Ealdorman of Berkshire. After one of the earls was killed and a large part of the Danish army was overthrown, the Viking force broke and ran.The victory was short-lived. Four days later, the main West Saxon army, led by King Ethelred and his brother, the future King Alfred the Great, attacked the main Danish encampment at Reading and were bloodily repulsed in the Battle of Reading. Among the many dead of both sides was Æthelwulf. Further battles followed, including the Battle of Ashdown, a West Saxon victory, and the Battle of Meretun, when the Danes prevailed. Soon after Easter, which fell on 15 April in that year, Æthelred died and was succeeded by Alfred.The Battle of Englefield can be dated because Bishop Heahmund of Sherborne died in the Battle of Meretun, and it is known that he died on 22 March 871. The Anglo-Saxon Chronicle records that the Battle of Basing was two months earlier, dating it to 22 January, Ashdown fourteen days before that on 8 January, Reading four days earlier on 4 January, Englefield another four days earlier on 31 December 870, and the arrival of the Vikings in Reading three days earlier on 28 December. However, as the two month interval between Meretun and Basing is probably not exact, the earlier dates are approximate.