Islam has dramatically spread from its founding in the early 7th century all the way now as we're exiting the 8th century to cover most of the Middle East, Persia, bordering on modern-day Pakistan, India, North Africa, and even going into modern-day Spain. At the same time, especially because of these Islamic conquests, the Byzantine Empire and the Byzantine emperor is significantly weaker. So you can imagine the pope in Rome here saying, well, who's going to protect me, especially from my political enemies? Now, Charlemagne considers himself something of a protector of Christianity, and Pope Leo III goes to him for protection, and Charlemagne is able to actually provide it. And in exchange, or perhaps in thanks for that, the pope crowns Charlemagne as Holy Roman Emperor. Now, what's significant about this is it really introduces a fourth actor here, because the title Holy Roman Emperor was intentionally given to say, look, now you, Charlemagne, you are the heir to the grandeur of Rome. You are the heir to the Roman emperors.