In Normandy, the Vikings adopted French culture and language, mixed with the native population of mostly Frankish and Gallo-Roman stock and became known as the Normans. They played a major political, military, and cultural role in medieval Europe and even the Near East. They were famed for their martial spirit and Christian piety. They quickly adopted the Romance language of the land they settled in, their dialect becoming known as Norman, an important literary language. The Duchy of Normandy, which they formed by treaty with the French crown, was one of the great large fiefs of medieval France. The Normans are famed both for their culture, such as their unique Romanesque architecture, and their musical traditions, as well as for their military accomplishments and innovations. Norman adventurers established a kingdom in Sicily and southern Italy by conquest, and a Norman expedition on behalf of their duke led to the Norman Conquest of England. Norman influence spread from these new centres to the Crusader States in the Near East, to Scotland and Wales in Great Britain, and to Ireland.