Oxford was first settled in Saxon times, and was initially known as "Oxenaforda", meaning "Ford of the Oxen"; fords were more common than bridges at that time. It began with the foundation of an oxen crossing in the early 900 AD period. In the 10th century Oxford became an important military frontier town between the kingdoms of Mercia and Wessex and was on several occasions raided by Danes.
Oxford was heavily damaged during the Norman Invasion of 1066. Following the conquest, the town was assigned to a governor, Robert D'Oyly, who ordered the construction of Oxford Castle to confirm Norman authority over the area. The castle has never been used for military purposes and its remains survive to this day. D'Oyly set up a monastic community in the castle consisting of a chapel and living quarters for monks (St George in the Castle). The community never grew large but it earned its place in history as one of the oldest places of formal education in Oxford. It is there that in 1139 Geoffrey of Monmouth wrote his History of the Kings of Britain, a compilation of Arthurian legends