Leo III

The Roman empire had not ceased to exist in 800. It was governed from Constantinople, and its throne was at that moment occupied by Irene, who had blinded and deposed her own son to take it. Western churchmen argued that a woman could not hold the imperial office and that the throne was therefore vacant, and it is in that gap that the events in Saint Peter's belong. During Mass on Christmas Day, Leo III crowned Charlemagne, king of the Franks and Lombards, and the congregation acclaimed him emperor of the Romans.

Einhard, Charlemagne's biographer, records that the king said afterwards he would not have entered the church that day had he known the pope's intention, a remark historians have read in opposite ways ever since: as genuine reluctance at receiving the crown from a bishop's hand, as unease at the diplomatic breach with Constantinople, or as a formula of modesty. Whatever he meant, the precedent set was that the pope crowns the emperor, and every medieval argument about whether the papacy therefore confers imperial authority begins here.

The consequences were not confined to the West. Constantinople regarded the coronation as usurpation and did not recognize a Western emperor for twelve years, and the two halves of Christendom, already drifting apart in language, liturgy and law, now had rival emperors as well as rival patriarchs. Leo himself had every reason to want a Frankish protector: in April 799 he had been ambushed in a Roman procession by nephews of the previous pope, who tried to blind him and cut out his tongue, and it was Charlemagne who sent him back to Rome under escort and came in person the following year to hear the charges against him.

The Nicene Creed as the councils issued it says that the Holy Spirit proceeds from the Father. Spanish and then Frankish churches had come to recite it with an added word, Filioque, and from the Son, and by the end of the eighth century the addition was normal in Charlemagne's chapel at Aachen. In 809 Frankish monks in Jerusalem were accused by Greek monks of heresy for singing the creed that way, and the dispute came to Rome. A synod at Aachen approved the addition and sent envoys to ask the pope to authorize it for the whole church.

Leo III gave an answer of unusual precision. He told the Frankish envoys that the doctrine the word expressed was sound and could be taught, and that the text of the creed itself must not be altered, because a council had settled its wording and no local church had authority to add to it. To make the ruling permanent he had the creed engraved in Greek and Latin, without the Filioque, on two silver shields and set up at the confession of Saint Peter, where anyone could read what Rome actually recited.

The distinction he drew, between a true teaching and an authorized text, held in Rome for about two centuries. The Filioque entered the creed at Rome only in the eleventh century, and by then it had become one of the standing grievances of the Eastern churches against the Western, cited in the mutual excommunications of 1054 and in every reunion negotiation since. Leo's shields are long gone, but his ruling is still quoted in ecumenical discussion as evidence that the Roman see once distinguished the two questions.