By Philip Daileader, William & Mary
Pope Leo III’s predecessor had been Hadrian I, pope from 772 to 795. There were some tensions in the relationship between Hadrian and Charlemagne. The Frankish absorption of the Lombard kingdom gave the Franks a strong presence in northern Italy and brought Charlemagne’s rule to the doorstep of the recently emerged papal state in central Italy, the Republic of Saint Peter.

Hadrian’s Successor, Leo III
Hadrian complained frequently that Frankish officials were not handing over lands that Charlemagne’s father, Pepin, had promised to the papacy. Even so, Hadrian and Charlemagne developed a good working and even a warm personal relationship. Charlemagne’s visits to Rome in 774, 781, and 787, had all gone well. Charlemagne grieved at Hadrian’s death in 795.
Hadrian had come from an aristocratic Roman family. His papal successor, who took the name of Leo III, did not come from an aristocratic family—instead, this future Pope Leo had worked his way up through the ranks. Moreover, Leo’s papal election had been conducted hastily, on the same day that Hadrian was buried.
Holding a quick election at a moment when Hadrian’s family was otherwise occupied may have been intended to limit the ability of Hadrian’s family and supporters to influence the election’s outcome. Hadrian’s family and supporters certainly disliked Leo after his election; they sought to undermine and end Leo’s pontificate.

Attack on Pope Leo III
By 798, stories were circulating in Charlemagne’s kingdoms about Leo’s less-than-spotless personal life. Rumblings about Leo started to appear in the letters of Alcuin, who was among the most important of Charlemagne’s courtiers. In 799, Alcuin received a letter from the archbishop of Salzburg regarding Pope Leo’s behavior. Alcuin found the letter’s contents so disturbing that he burned the letter.
Then, on 25 April 799, Leo’s opponents attacked the pope as he led a religious procession through the streets of Rome. The attackers assaulted the pope, mutilating his face; they also dragged him to a monastery, where they stripped him of his papal garments and proclaimed that the former Pope Leo no longer held the papal office. Not long thereafter, his captors tried to transfer Leo to a different monastery, but he managed to escape, presumably with the help of others.
Pleadings to Charlemagne
Leo fled to the Kingdom of the Franks and sought out Charlemagne; those who had attacked Leo sent their own ambassadors to Charlemagne, looking to plead their case.
Charlemagne, hearing that both Leo and ambassadors representing Leo’s attackers were headed his way, awaited their arrival at Paderborn in Germany.
Leo reached Paderborn first, most likely in the middle of September 799. When the attackers’ representatives arrived, they argued that Leo’s behavior had driven them to depose him. Specifically, they accused Leo of fornication. Because Leo III had denied the accusation under oath, his enemies accused Leo of perjury as well.
Charlemagne’s Thoughts about the Accusations
What Charlemagne thought of these accusations can only be surmised, and there were many factors to consider. On the one hand, Charlemagne probably knew well those who had attacked and deposed Leo. They came from leading families, and they had held high office while in the service of Pape Hadrian, with whom Charlemagne’s rapport had been good. Moreover, their accusations were not far-fetched.
On the other hand, could one countenance physical assault and the facial mutilation of a pope under any circumstances? Even if Leo’s behavior was improper, any besmirching of the papacy’s reputation might have had consequences for the legitimacy of Carolingian rule.
The pope had sanctioned the coup in 751 that had made Charlemagne’s father king; another pope anointed Pepin as king in 754. Because papal support had been instrumental in the Carolingian accession to kingship, papal disgrace was a potential threat to continued Carolingian rule.
At a more practical, concrete level, Pope Leo had been just as deferential to Charlemagne as Hadrian had been. About the cooperativeness of Leo’s successor, there could be no guarantees.
This is a transcript from the video series Charlemagne: Father of Europe. Watch it now, on Wondrium.
Who Could Judge the Pope?

Leo returned to Rome in November 799, accompanied by Frankish bishops tasked with investigating the accusations against Leo.
The bishops investigated and then, based on their findings, they declined either to substantiate or to dismiss the accusations. They may have refused to pronounce one way or the other regarding Leo‘s guilt simply to avoid controversy, but there was also a procedural and jurisdictional problem.
Who, if anyone, could sit in judgment of a pope? Some of Charlemagne’s courtiers, including Alcuin, weighed in and opined that no human being, not even Charlemagne, could presume to judge a sitting pope. But if no human being could judge a pope, then how could this situation be resolved?
Leo resumed his papal duties upon his return to Rome, but his accusers continued to insist on the truth of their accusations and the necessity of deposing Leo. In November 800, a year after Leo’s return to Rome, Charlemagne himself made his fourth visit to Rome.
Time to Face the Consequences
On December 23, 800, Pope Leo III cleared his name by swearing an oath and attesting that he was innocent of the crimes of which he had been accused.
Given that Leo had been accused of perjury, allowing him to clear his name by swearing an oath was setting the bar rather low. But it was high enough for Charlemagne—case closed, almost. Charlemagne still needed to deal with those who had accused and attacked the pope; justice had to be done.
Charlemagne ordered a punishment of death; Leo intervened, asking for mercy on behalf of the condemned; Charlemagne agreed, and commuted the punishment to exile in the Kingdom of the Franks. Without doubt, Charlemagne orchestrated this outcome and this sequence of events. Charlemagne came across as both tough on crime and merciful.
Common Questions about the Intense Accusations Against Pope Leo III
The main accusation against Pope Leo III was fornication, but since he swore under oath that he was innocent, he was also accused of perjury.
The bishops may have refused to pronounce one way or the other regarding Leo‘s guilt to avoid controversy. However, there was also a procedural and jurisdictional problem. It was believed that no human being, not even Charlemagne, could presume to judge a sitting pope.
After Pope Leo III’s name was cleared, Charlemagne ordered the death of the accusers. However, Leo intervened, asking for mercy on behalf of the condemned, to which Charlemagne agreed, and commuted the punishment to exile in the Kingdom of the Franks.