Many a time already the Popes had rendered the Frankish kings this service and honor.

The Franks had been proud to see their king, Charlemagne, protecting Adrian I.against the Lombards; then crowned emperor at Rome by Leo III., and then having his two sons, Pepin and Louis, crowned at Rome, by the same Pope, kings respectively of Italy and of Aquitaine.

On these different occasions, Charlemagne, whilst testifying the most profound respect for the Pope, had, in his relations with him, always taken care to preserve, together with his political greatness, all his personal dignity.

But when, in 816, the Franks saw Louis the Pious not only go out of Rheims to meet Stephen IV., but prostrate himself, from head to foot, and rise only when the Pope held out a hand to him, the spectators felt saddened and humiliated at the sight of their emperor in the posture of a penitent monk.
Several insurrections burst out in the empire; the first amongst the Basques of Aquitaine; the next in Italy, where Bernard, son of Pepin, having, after his father's death, become king in 812, with the consent of his grandfather Charlemagne, could not quietly see his kingdom pass into the hands of his cousin Lothaire at the orders of his uncle Louis.

These two attempts were easily repressed, but the third was more serious.