Lothair, Emperor Louis’ eldest son by Ermengarde, is the heir to the entire Carolingian Empire, but has to share it with his brothers because of the traditional Frankish practice of division of patrimonies among all surviving sons.

Lothair had probably passed his early life at the court of his grandfather Charlemagne, until 815 when he became king of Bavaria.

When Louis divided the Empire between his sons in 817, Lothair had been crowned joint emperor at Aix-la-Chapelle (Aachen) and given a certain superiority over his brothers, Pepin and Louis, who had respectively received Aquitaine and Bavaria.

Lothair was also given the Iron Crown of Lombardy, then still held by Louis the Pious' nephew Bernard.

After Bernard’s death, Lothair had received the Italian kingdom.

In 821, he had married Ermengarde, daughter of Hugh, count of Tours, and in 822 assumed the government of Italy.

On April 5, 823, he had been crowned co-emperor again by Pope Paschal I, this time at Rome.

In November 824, he promulgates a statute concerning the relations of pope and emperor which reserves the supreme power to the secular potentate, and from this time he is to issue various ordinances for the good government of Italy.