In 781, Charlemagne established sub kings for his domain and appointed Louis I as king of Aquitaine. He was three years old. As king, Louis had his own palaces, chancery, treasury, and mints. He became co-emperor with his father in 813. He already had 35 years experience as a politician and military commander. His domain stretched from the now cities of Hamburg, Germany to Barcelona, Spain and from Nantes, France to Osnabruck, Germany. This 'First Europe' had many different ethnic, langauage, and cultural societies. It included Franks, Saxons, Bretons, Aquitanians, Spaniards, Lombards, Jews, Byzantines, Romands, Bavarians, Avars, Slavs, and others. He commanded military expeditions and supervised the Frankish counts, abbots, and vassals that were sent to Aquitaine.

A Septimanian Visigothic nobleman and monastic founder whose name was Benedict of Aniane, helped Louis reform the Frankish church. The reforms would ensure that all religious houses in Louis' realm would adhered to the Rule of St. Benedict.

Louis shared the kingdom with his two brothers but when both of them died before he, Louis inherited all of the Frankish empire. He secured his position as emperor by sending all of his half brothers to monasteries and his unmarried sisters to nunneries. His nephew Bernard, King of Italy, rebelled against his overlordship, and after suppressing the rebellion, he had Bernard blinded and imprisoned. Bernard died the next year. As a deeply religious man, however, Louis wanted to make penance for causing Bernard's death, and did so at Attigny in 822, in front of the nobles of the realm.

In 817 Louis formed plans for his succession by dividing the empire between his three sons from his marriage to Ermengarde. Lothair was crowned king of Italy and Co-emperor; Pepin was king of Aquitaine; and Louis II was king of Bavaria.