Oxford was founded in the 9th century when Alfred the Great created a network of fortified towns called burhs across his kingdom. One of them was at Oxford. Oxford is first mentioned in 911 in the Anglo-Saxon Chronicle.
According to legend, Oxford University was founded in 872 when Alfred the Great happened to meet some monks there and had a scholarly debate that lasted several days. In reality, it grew up in the 12th century when famous teachers began to lecture there and groups of students came to live and study in the town.
But Oxford was a fortress as well as a town. In the event of war with the Danes all the men from the area were to gather inside the burgh. However this strategy was not entirely successful. In 1009 the Danes burned Oxford. However Oxford was soon rebuilt. In 1013 the Danish king claimed the throne of England. He invaded England and went to Oxford. In 1018 a conference was held in Oxford to decide who would be the king of England.
By the time of the Norman Conquest, there were said to be about 1,000 houses in Oxford, which meant it probably had a population of around 5,000. By the standards of the time, it was a large and important town (even London only had about 18,000 inhabitants).