Pope Leo's plan required he get Charlemagne into the church. To do this, he pretended to be grateful to Charlemagne and asked Charlemagne to kneel with him in prayer. They did this on Christmas Day, in the year 800 CE. With hundreds of people watching while Charlemagne knelt down Pope Leo placed a crown on Charlemagne's head, and in front of everyone proclaimed Charlemagne the first Holy Roman Emperor
The people cheered and shouted. Their King, Charlemagne, was now an Emperor by decree of the Pope. This seemed to the people to be the ultimate honor. Charlemagne knew better.
Charlemagne was no fool. He knew that the title, Holy Roman Emperor, actually placed him under the command of the church. For the rest of his life he did not use the title Holy Roman Emperor, but instead used the title Emperor of the Franks and Lombards.