By the middle of the eighth century, the Merovingian dynasty that had ruled the Franks for nearly three hundred years survived in name only. Real power had passed generations earlier to the Mayors of the Palace, and by 751 Pepin the Short held every function of a king, commanding the army, dispensing justice, and controlling the treasury, while Childeric III, the reigning Merovingian, held the title alone. Pepin, unwilling simply to seize the crown without any higher sanction, sent envoys to Pope Zachary in Rome with a carefully framed question, whether it was proper for the man who held no royal power to bear the title of king, rather than the man who exercised it.
Zachary's answer, that it was better for the one with the power to hold the name of king, gave Pepin the sanction he needed. Childeric III was deposed and sent to a monastery, and Pepin was elected and anointed king of the Franks by the assembled nobility, with Boniface, the missionary archbishop working under papal authority in Frankish territory, playing a leading role in the anointing according to most accounts of the events.
The ruling had consequences neither Zachary nor Pepin could have fully foreseen. Pepin's son Charlemagne would build the Frankish kingdom into an empire crowned by Zachary's own eventual successors, and the precedent that a pope could pronounce on the legitimacy of a European throne became one of the medieval papacy's most consequential political tools, invoked and contested for centuries afterward.