What happened
On Christmas Day in Rome, Charlemagne was crowned emperor by Pope Leo III. The coronation revived a western imperial title centuries after the collapse of the Western Roman Empire.
Why it matters
This event is one of the key predecessors to the Holy Roman imperial tradition. It did not create the Holy Roman Empire in the later conventional sense, but it established a western medieval claim to Roman imperial authority that later rulers inherited and reinterpreted.
Notes
If 962 marks the conventional beginning of the Holy Roman Empire proper, 800 marks the most important earlier western revival of empire from which that later tradition drew legitimacy.