In his relations with the Church, Charles gave a liberal interpretation to his acknowledged powers of guidance and direction; the kind of rôle he was willing to undertake shows that he drew no hard and fast line between the secular and spiritual prerogatives of a monarch. For example, in the Adoptionist Controversy, he took the initiative himself in settling a troublesome problem of theological speculation. According to the Adoptionists, in Christ there are a divine personality and a human personality, which latter becomes by adoption the Son of God. This tenet was eagerly embraced in Spain, its two best-known adherents being Elipandus, Archbishop of Toledo, and Felix, Bishop of Urgel, the latter a city in the North of Spain under the authority of the Frankish King, who, therefore, immediately took steps to bring the subject in dispute before a council, assembled at Regensburg, “under the orders of the most glorious and orthodox King Charles.” Felix was convicted of false teaching and sent to Rome to appear before Pope Hadrian. Though Felix was deprived of his bishopric he continued to be supported by the Spanish episcopate, who collectively wrote to Charles for his restoration. At Frankfort, in 794, a council of prelates from various Frankish sees met and listened to the King, who read the letter from the Spanish bishops. The council then heard a long technical speech from their ruler on the questions at issue. The Bishop of Urgel was again condemned, but the matter was not decided until a few years later, in 799, when a long discussion, lasting over six days, took place at Aix between Felix and Alcuin, the conclusion of which was that Felix allowed that he was overcome in argument, and published a retraction.

Charles was equally interested in two other religious controversies of his time, and he made his personal point of view predominant in spite of the weight of church authority on the other side. At the Council of Frankfort the bishops had received from Pope Hadrian the acts passed at the Second General Council of Nicæa dealing with the subject of image worship, a matter that had been debated with much violence in the East and in Italy for several generations. At Frankfort it was supposed, owing to an inability to understand the precise meaning of certain Greek words, that the Nicene Council had formally ordered the adoration of images, and its decrees were therefore rejected. The Emperor undertook the defense of the Western point of view, and in doing so did not hesitate to differ with Rome itself. He also took up an independent position on a more vital point. It seems that during Leo III’s pontificate certain French monks residing in the East were charged with heresy because they inserted in the so-called Nicene Creed, in the article dealing with the procession of the Holy Spirit, i.e., where it is stated that the Holy Spirit proceeds from the Father, the crucial word “filioque” (and from the Son). The matter was taken up by Charles, and after this recondite theological point had been studied, the action of the monks was officially sanctioned by the Council of Aix-la-Chapelle, in 809, although the Pope refused to approve of any addition to the historic formula of Christian belief.

In considering the Frankish ruler’s attitude towards the Papacy, it is well to remember that the later administrative system of the Curia, which made so clear-cut the antagonism between the secular prince and the ecclesiastical hierarchy in the medieval times after the age of Hildebrand, had not yet been developed. Charles reverenced the Papacy; indeed, the Pope’s counsel and the Pope’s words often played a decisive part in influencing his motives. He was a convinced believer in the Pope’s right to teach the faithful, and he saw in him the guardian of apostolic tradition. It was to this tradition that he appealed when he condemned the Adoptionists at the Council of Frankfort. The specific rights of the Papacy, from this point of view, lay in its teaching function and in its liturgical usages, which were to be taken by the Christians of Charles’ dominions as the correct norm of their practice. There was also a full recognition of the prerogatives of the Papacy in phases of administration and discipline, wherever ancient precedents could be cited. So we find Charles appealing, in the renewed disputes between the sees of Arles and Vienne, to the ancient directions of the Roman bishops governing this question.

But this recognition of the rights of Rome did not prevent Charles from regarding himself as the director of the Frankish Church. He speaks openly of himself as “the pilot of the Church in his domains,” and when writing Leo III he explains his conception of the relation of the kingdom and the Papacy. “Our task it is, by the help of God, to protect by our arms outwardly the Holy Church of Christ from assaults of the heathen and from being wasted by the unbelievers and to establish it within by recognizing the Catholic faith. Your duty it is to support as Moses did, with uplifted arms our service in the battlefield, that the Christian people, being led through your petitions and prepared by God, may have constantly and everywhere victory over the enemies of His name.” While Charles assigned to the Pope a religious activity and nothing more, he regarded his own guardianship over the churches as extending beyond questions of their material welfare. In 789 in a message to the bishops he stated that he wished to coöperate with them, using his power as a ruler, and working through his subordinates to improve things where improvement was possible. These were the principles he used in his Church policy. Just as in secular matters he was not absolute, but followed the laws and customs of the people over whom he ruled, so in regard to the Church he observed its canonical system with a reverence for its minute details. But his capitularies, as we have seen, are filled with ecclesiastical legislation, and in Church matters the King acted as the supreme authority. Even synods laid their decrees before him for correction, and to secure his authoritative sanction. There was little place for a fully developed Papacy in an ecclesiastical system worked along these lines, and there are no examples during Charles’ reign of Papal interference in the administration of the Church in his own domains. The Pope, where and when he did act, did so in concert with Charles; even in cases of excommunication there was an understanding with the King; and often the extreme penalty was inflicted under his initiative. Even the exercise of discipline in connection with the episcopate was left in Charles’ hands without any protest on the part of the Pope.

These religious activities of Charles seemed natural to his contemporaries. Alcuin says of him that he was armed with two swords, the one to smite false teaching in the bosom of the Church, the other to protect it from the devastations of the heathen. He speaks of Charles as a parent and teacher, under whose rule the Church is placed; yet at the same time Alcuin had the highest reverence for the Papacy and never thought of the possibility of conflict between the Pope and the Emperor. In Rome itself there was no formal acceptance of this Frankish conception of an ecclesiastical polity in which the Pope’s place was that of a fifth wheel to the coach. Roman enthusiasm for the Emperor, as expressed by the Roman clergy, was limited to encomiums on him as protector of the Church. He was spoken of as the faithful ruler, who, by his energy and his benefactions, was doing valiant work for Rome and for the Papacy.

In matters of internal Church administration, the influence of the King was often paramount in questions affecting diocesan order. There was nothing revolutionary here, for the independence of the Church from the State implied a situation that was never dreamed of at this period, nor had it really existed since the time of Constantine. Theoretically, the choice of a bishop belonged rightfully to the clergy and to the laity of a diocese, but, as a matter of fact, the monarch controlled episcopal elections. These could not take place until the royal sanction had been secured, and the official in whose presence the electoral machinery was set in motion was an appointee of the King. The official papers recording the election had to be sent to the palace, and the successful candidate could not be consecrated except with the King’s approval. Often Charles himself selected the candidate; besides, if a man were known to be favored by him, he would, on the strength of this fact, be elected. Where bishops were to be appointed for sees created in territory newly conquered from the heathen, they were named by Charles without the form of an election. What is true of bishops holds also with regard to abbots, who, on account of the great expansion of monastic life, were of more importance than a diocesan bishop. Church councils were summoned by Charles; he could preside over them, and only through his consent were the decrees they passed valid. Much attention was given to a systematic organization of the hierarchy. There were twenty-two metropolitical sees in the Empire, and the bishop was given real and effective charge of the clergy under him. Counties and parishes, throughout the imperial domains especially, were growing in number, and were placed in the newly acquired territories under an assistant bishop.