The Normans, also known as the Normaunds, were a medieval Franco-Norse people native to the Normandy region of northern France. The word "Norman" derives from "Northman", referring to the Norse Vikings under Rollo who were allowed to settle in the lower Seine valley by King Charles the Simple of West Francia in 911 AD. Rollo and his descendants were vassals of the Frankish king, and they were obliged to defend northern France against other Viking attacks. Over the years, the Norsemen assimilated into the French culture, adopting the French language and the Catholic faith, but they also maintained their ancestors' warlike nature, forging a hybrid Franco-Norse culture. During the early 11th century, the Normans made a reputation for themselves as the best mercenaries in Southern Europe, acquiring a power base in southern Italy as the result of their participation in several local conflicts. In 1066, the Norman duke William the Conqueror seized the throne of England from the Anglo-Saxon king Harold Godwinson at the Battle of Hastings, and he proceeded to forcefully assert Norman rule over England as late as the 1070s, building motte-and-bailey castles to bring the Saxon peasants to heel and launching the "Harrowing of the North" to crush Dano-Saxon resistance to his rule. By the 1080s, 95% of English land south of the Tees River was owned by Normans, and, over the next few centuries, the intermarriage of Norman elites and Saxon peasants led to the creation of a newer hybrid culture, the English, whose language had both Romance (from the Normans) and Germanic (from the Saxons and Danes) influences. The Norman conquest of England was followed by the Norman invasion of Ireland, after which several Norman knights were enfeoffed in eastern Ireland, creating a new "Hiberno-Norman" culture in the form of Norman names such as Fitzgerald, Burke, and Barry, among others. Other Normans established themselves in South Wales and Scotland. Norman culture later spread east due to the Crusades, during which several Norman and Anglo-Norman knights took up the cross and created new domains for themselves in the Levant.
The Norman culture soon became obsolete outside of northern France, as the Normans in the British Isles assimilated into the local English, Welsh, Scottish, and Irish cultures, the Normans of Apulia and Calabria were conquered by the Holy Roman Empire in 1194, and the Norman knights in the Levant and their fellow Latin-speaking crusaders adopted a new "Outremer" culture. The Normans outside of France assimilated into local cultures, bringing with them their surnames and aspects of their music and language, and the Norman language still survives in Normandy in northern France and the Channel Islands of the United Kingdom.