800–809

Coronation of Charlemagne and the Aachen Filioque Dispute

On Christmas Day 800, Pope Leo III crowned Charlemagne emperor. This restored a Western empire under the church's aegis for the first time since the fall of the last Western Roman emperor. Shortly before, a Roman synod had cleared Leo of his opponents' accusations.

The coronation raised the papacy's prestige. But it also set up a future dispute over whether imperial power depended on papal coronation. Constantinople's protest was ignored, which deepened the East-West divide.

In 809 a Frankish synod at Aachen declared the Greek formula of the creed without the Filioque addition heretical. At Aachen the creed was already sung with the Filioque. Pope Leo III accepted the Filioque doctrine but refused to insert the words into the Nicene Creed's text.

After Charlemagne's death in 814 his empire did not hold together. Strife broke out among the sons of Louis the Pious. It ended in 843 with the Treaty of Verdun, which split the realm into three parts.