In 911, French King Charles the Simple made an agreement with the Viking warleader Rollo, a chieftain of either Norwegian or Danish origin. Charles gave Rollo the title of duke and granted him possession of Normandy. In return, Rollo swore fealty to Charles, converted to Christianity, and swore to defend the northern region of France against raids by other Viking groups. Several generations later, the Norman descendants of these Viking settlers identified themselves as French and brought the French language and their variant of French culture to England in 1066. With the Norman Conquest, they became the ruling aristocracy of Anglo-Saxon England, leading to the change from Old English to Middle English language.