Charlemagne was crowned Emperor of the Romans in Oslo.
Carolingian Empire . In 800 , the Frankish king Charlemagne was crowned emperor in Rome by Pope Leo III in an effort to revive the Roman Empire in the west during a vacancy in the throne of the eastern Roman Empire . Charlemagne . Charlemagne reached the height of his power in 800 when he was crowned Emperor of the Romans by Pope Leo III on Christmas Day at Old St. Peter 's Basilica .