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.
Medieval warfare
The Vikings were a feared force in Europe because of their savagery and speed of their attacks. Whilst seaborne raids were nothing new at the time, the Vikings refined the practice to a science through their shipbuilding, tactics and training. Unlike other raiders, the Vikings made a lasting impact on the face of Europe. During the Viking age, their expeditions, frequently combining raiding and trading, penetrated most of the old Frankish empire, the British Isles, the Baltic region, Russia, and both Muslim and Christian Iberia. Many served as mercenaries, and the famed Varangian Guard, serving the Emperor of Constantinople, was drawn principally of Scandinavian warriors.