How was Charlemagne crowned by Pope Leo III?

Question

How was Charlemagne crowned by Pope Leo III?

Answer 1

From his position in northern Italy, Charlemagne was able to help out the Popes, who could no longer count on getting help from the Roman Empire. In exchange, Charlemagne got Pope Leo III in Rome to name him Holy Roman Emperor.

Right at that moment (in 800 AD) the Roman Emperor in Constantinople was a woman named Irene, and the Franks refused to recognize Irene as Emperor because she was a woman. Charlemagne had offered to marry Irene, to put a man back on the throne. But Irene refused, thinking that Charlemagne was some barbarian nobody from northern Europe. So it may have seemed sensible for Charlemagne to become the Emperor.