Three groups invaded the Carolingian Empire between 700-800 CE: seafaring Scandinavian invaders called Vikings; Germanic peoples also called Norsemen; and nomadic horsemen from the East called Magyars. In 911 CE, the Viking ruler Rollo and the Frankish ruler Charles the Simple signed an agreement granting Rollo land in Normandy in exchange for his loyalty, establishing the foundation of feudalism. By the mid-900s, the German king Otto the Great had become a new defender of Christendom against invaders, following in Charlemagne's footsteps to become Holy Roman Emperor.