Charlemagne united a large part of Europe during the early Middle Ages and established the first empire after the fall of the Western Roman Empire. As King of the Franks, he laid the foundations for modern France and Germany by expanding the Frankish realm under his powerful rule. The capital of Charlemagne's empire was Aachen, located in a central position between the western and eastern parts of the empire, which became an important center of education and culture. After Charlemagne, his son Louis the Pious ruled as King of Aquitaine and co-Emperor with his father, and his three sons Louis the German, Charles the Bald, and Lothair later inherited parts of the Carolingian Empire.