Irene of Athens
Two days after his oath, on Christmas Day 800, Leo crowned Charlemagne as emperor. According to Charlemagne's biographer, Einhard, Charlemagne had no suspicion of what was about to happen, and if informed would not have accepted the imperial crown. There is, however, no reason to doubt that for some time previous the elevation of Charlemagne had been discussed, both at home and at Rome, especially since the imperial throne in Constantinople was controversially occupied by a woman, Irene of Athens, and since the Carolingian dynasty had firmly established its power and prestige. The coronation offended Constantinople, which had seen itself still as the rightful defender of Rome, but Empress Irene, like many of her predecessors since Justinian I, was too weak to offer protection to the city or its much reduced citizenry.