Charlemagne was crowned in Vatican City.
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.
Old St. Peter 's Basilica was the building that stood , from the 4th to 16th centuries , on the spot where the new St. Peter 's Basilica stands today in Vatican City.
