A Crown From the Pope on Christmas Day

Charlemagne's coronation in Rome on Christmas Day 800, when Pope Leo III placed an imperial crown on the Frankish king's head, revived a Western imperial title that had lapsed more than three centuries earlier and bound it explicitly to papal endorsement. A history of the empire that grew from this act treats the coronation as less a single dramatic event than the culmination of a partnership decades in the making: Charlemagne's father Pepin the Short had already intervened militarily to protect the papacy from Lombard attack and had granted the pope territory in central Italy, the beginning of what became the Papal States, in exchange for a papal anointing of his own kingship in 754.

The 800 coronation made that alliance formal at the highest possible level, and it set a precedent that shaped Western political theology for centuries afterward: a Western emperor's legitimacy now ran, at least in the form the ceremony asserted, through papal approval rather than through Frankish military power alone. The precedent proved durable well past the Carolingian dynasty's own decline in the following century, since German kings from Otto I onward revived and claimed the same imperial title, crowned in Rome by the same office, founding what later became known as the Holy Roman Empire on a template Charlemagne's coronation had set.