Louis I (778-840), or Louis the Pious, was king of the Franks and emperor of the West from 814 to 840. The son and successor of Charlemagne, he was the last ruler to maintain the unity of the Carolingian Empire.

Born in Aquitaine, Louis I was the third son of Charlemagne and his second wife, Hildegard. Most of his youth was spent in Aquitaine, where he received a clerical education of high quality. In 806 Louis, along with his brothers, Charles and Pepin, was assigned to his inheritance, being designated king of Aquitaine. His brothers received equal territories within the empire. At this time Aquitaine included Burgundy and the Spanish March; however, it was in no sense independent of the overlordship of Charlemagne.

Between 806 and the death of Charlemagne in 814, Charles and Pepin died, leaving Louis, the least aggressive and warlike of the three, as the sole heir to the empire...