What was the formal role of the emperor title of Charlemagne?

Pope Leo III crowned the Frankish king, Charlemagne, Emperor of the Romans on Christmas Day, 800 in St. Peter's Basilica in Rome, making him the most powerful ruler of his time. ... When the pope bestowed the title of emperor on him, the Roman empire lived on in Charlemagne. read more

Similarly, Lombardia was ruled by Charlemagne as the King of the Lombards, the title he took from Desiderius. The coronation of Emperor made Charlemagne the protector of the the Christian Church and thus added ecclesiastical support to his rulership. read more

Charlemagne (c.742-814), also known as Karl and Charles the Great, was a medieval emperor who ruled much of Western Europe from 768 to 814. In 771, Charlemagne became king of the Franks, a Germanic tribe in present-day Belgium, France, Luxembourg, the Netherlands and western Germany. read more