Ulster, a serious attack was made on Lindisfarne's mother-house of Iona, which was followed in 795 by raids upon the northern coast of Ireland. From bases there, the Norsemen attacked Iona again in , causing great slaughter amongst the Céli Dé Brethren, and burning the abbey to the ground. The Vikings primarily targeted Ireland until 830, as England and the Carolingian Empire was able to fight the Vikings off. However, after , the Vikings had considerable success against England, the Carolingian Empire, and other parts of Western Europe. After 830, the Vikings exploited disunity within the Carolingian Empire, as well as pitted the English kingdoms against each other. The Kingdom of the Franks under Charlemagne was particularly devastated by these raiders, who could sail up the Seine with near impunity. Near the end of Charlemagne's reign (and throughout the reigns of his sons and grandsons), a string of Norse raids began, culminating in a gradual Scandinavian conquest and settlement of the region now known as Normandy in 911. French King Charles the Simple granted the Duchy of Normandy to Viking warleader Rollo (a chieftain of disputed Norwegian or Danish origins) in order to stave off attacks by other Vikings. Charles gave Rollo the title of duke. In return, Rollo swore fealty to Charles, converted to Christianity, and undertook to defend the northern region of France against the incursions of other Viking groups. Several generations later, the Norman descendants of these Viking settlers not only identified themselves as Norman, but also carried the Norman language (either a French dialect or a Romance language which can be classified as one of the Oïl languages along with French, Picard and Walloon), and their Norman culture, into England in 1066. With the Norman Conquest, they became the ruling aristocracy of Anglo–Saxon England. The clinker-built longships used by the Scandinavians were uniquely suited to both deep and shallow waters. They extended the reach of Norse raiders, traders, and settlers along coastlines and along the major river valleys of north-western Europe. Rurik also expanded to the east, and in 859 became ruler either by conquest or invitation by local people of the city of Novgorod (which means "new city") on the Volkhov River. His successors moved further, founding the early East Slavic state of Kievan Rus' with the capital in Kiev. This persisted until 1240, when the Mongols invaded Kievan Rus'. Other Norse people continued south