North Germanic peoples
Vikings were also active in Francia. Some of these Vikings would sail through the Strait of Gibraltar and pillage the coasts of the Mediterranean Sea. In the early 10th century, a group of Vikings under the leadership of Rollo settled in Rouen, France, and established the Duchy of Normandy. The descendants of these Vikings, known as the "Normans", would in the 11th century conquer England, Southern Italy, and North Africa, and play a leading role in launching the Crusades. Sub-groups of the Normans include Anglo-Normans, Scoto-Normans, Cambro-Normans, Hiberno-Normans and Italo-Normans.
Viking raid warfare and tactics
The Vikings were also able to establish an extended period of economic and political rule of much of Ireland, England, and Scotland during the Norse Ivarr Dynasty that started in the late 9th century and lasted until 1094. In Ireland, coastal fortifications known as longphorts were established in many places after initial raidings, and they developed into trading posts and settlements over time. Quite a few modern towns in Ireland were founded in this way, including Dublin.