The Secret History of Emperor Justinian

On December 23rd, 800, Pope Leo stood in front of the congregation assembled at St. Peter's and performed the oath of purgation. Two days later, on December 25th, Charlemagne celebrated Christmas in Rome. As he rose, Pope Leo came to his side, and as the royal Frankish annals describes it, quote, "...placed a crown on his head, and he was acclaimed"