Louis I (778-840), also known as Louis the Pious, Louis the Fair and Louis the Debonaire, was the sole surviving adult son of Emperor Charlemagne and Hildegard. Louis ruled from Aquitaine, charged by his father with defending the empire's southwestern frontier from the Muslims of Spain. He conquered Barcelona in 801 and asserted Frankish dominance over Pamplona and the Basques south of the Pyrenees in 812. He was named as co-emperor and King of the Franks by his father in 813, before becoming sole ruler in 814.