Vikings, or Norsemen, who settled in France; the population of the duchy of Normandy in northern France, a mixed race descending from the Franks and 10th-century Norse settlers of Denmark, Norway, and Iceland. In AD 1066, their leader, William of Normandy, conquered England, then Wales, Scotland, and Ireland. The Normans also conquered Sicily and southern Italy in a volatile period that began in 1063. These military feats were consolidated by the strength of the Norman feudal aristocracy and their skill in erecting strong, expedient fortifications ranging from motte and bailey earthworks to substantial stone castles. The Normans were also the main force behind the Crusades, which began in the 11th century AD. They promoted the French language and French culture, and the Romanesque style of architecture. By 1200 the Norman conquerors had been absorbed into the countries they ruled, but many of their institutions lasted into the late Middle Ages. Despite their eventual conversion to Christianity, their adoption of the French language, and their abandonment of sea-roving for Frankish cavalry warfare in the decades following their settlement in Normandy, the Normans retained many of the traits of their piratical Viking ancestors. They were restless, reckless, and loved fighting; they extended the practice of centralized authoritarian rule, feudalism, cavalry warfare, and religious reform.