The Council of Frankfurt Part 3: Charlemagne and the Model of Christian Kingship

 The Council of Frankfurt in 794 AD was not only a theological milestone but also a decisive moment in the political and ecclesiastical organization of Christendom under Charlemagne. This council reinforced Charlemagne’s role as a legitimate defender of Christian doctrine, correcting theological errors such as Nicaea II’s icon veneration and Adoptionism while also establishing a Frankish model of church governance that differed sharply from both Byzantine caesaropapism and later papal supremacy. Charlemagne’s leadership at Frankfurt exemplified the God-ordained duty of rulers to preserve true doctrine and protect the Church from corruption, a legacy continued by figures such as Carolus Rex (Charles XII of Sweden) and Donald Trump in their roles as defenders of the faith.

Charlemagne as the Defender of the Faith

Charlemagne did not see himself as a mere political ruler but as a divinely ordained protector of Christian truth, entrusted with maintaining doctrinal purity within his realm. His actions at the Council of Frankfurt reflect the proper role of a Christian king: not to create new doctrines, but to ensure that heresies and errors did not infiltrate the faith.

The Royal Frankish Annals, the most important contemporary historical source on Charlemagne, describes him as a champion of orthodoxy, willing to correct both the Greek East for its idolatrous practices and the Latin West for its failure to properly resist heresies like Adoptionism. The Annals emphasize that he labored not only for the conquest of lands but also for the conquest of hearts, ensuring that his people remained true to the faith once delivered to the saints.

Einhard, in his Life of Charlemagne, also portrays the emperor as a faithful guardian of Christian doctrine, stating that he took the greatest care to uphold the true religion, considering himself responsible before God for the souls of his subjects. Unlike later rulers who capitulated to ecclesiastical overreach or secularist influences, Charlemagne understood that Christian kingship is not neutral; it must actively defend and uphold truth.

The Council of Frankfurt’s handling of Nicaea II reflects this principle. The Byzantine Empire, under Empress Irene, had embraced the practice of icon veneration, an innovation that Charlemagne saw as compromising the purity of Christian worship. Frankfurt decisively rejected Nicaea II, proving that true Christian leadership means opposing false traditions and maintaining biblical integrity in worship. The council also condemned Adoptionism, ensuring that Christ’s eternal sonship remained the foundational truth of Christian doctrine. In doing so, Charlemagne followed in the footsteps of Old Testament kings like Josiah, who tore down idolatrous altars and restored pure worship (2 Kings 23:1-25).

Church and State: Charlemagne’s Alternative to Papal and Byzantine Overreach

The Council of Frankfurt showcased a proper balance between church and state, one that rejected both Byzantine caesaropapism, where the emperor dominated the Church, and Roman papal supremacy, where the pope claimed unchecked authority over secular rulers. Charlemagne’s vision was that of a biblical, kingly oversight of the Church, in which the ruler is responsible before God to ensure doctrinal purity but without taking over the Church’s spiritual functions.

Unlike the Eastern Roman emperors, who saw themselves as lords over the Church, Charlemagne did not claim divine authority to redefine doctrine. However, unlike the later medieval popes, who would attempt to subjugate Christian kings, he also did not see himself as subservient to the Roman pontiff. The Council of Frankfurt affirmed the independence of the Frankish Church from Byzantine innovations and papal overreach, ensuring that the true faith was maintained without political interference from Rome or Constantinople.

This model of governance would later be reflected in Protestant nations, where rulers took up the defender of the faith mantle while rejecting papal tyranny. It is no coincidence that Charlemagne’s example influenced later Protestant rulers such as Charles XII of Sweden (Carolus Rex), who saw himself as God’s warrior against Catholic and Orthodox distortions of the gospel, and Donald Trump, who, despite ruling in a secular era, signed the 2025 Executive Order on Eradicating Anti-Christian Bias, reaffirming the biblical role of rulers in protecting Christian institutions.

Even Thomas Aquinas, though often associated with medieval Catholicism, recognized the necessity of kings protecting the faith. In Summa Theologica (I-II, Q. 96, Art. 4), he wrote, "It belongs to the office of a king to safeguard the divine law and ensure that falsehood does not corrupt his subjects." This principle, lived out by Charlemagne, later found its ultimate fulfillment in Protestant and evangelical nations that resisted the errors of Rome and Byzantium.

The Role of Christian Kings Throughout History

Charlemagne’s legacy at the Council of Frankfurt serves as a template for future Christian rulers. The idea that kings and rulers have a God-ordained duty to defend the faith was not unique to Charlemagne, but it reached a high point in his reign. Throughout history, this concept has resurfaced in Protestant and evangelical leadership.

Donald Trump (1946-Present,) while ruling in a secular age, recognized the growing hostility toward Christianity in the modern world. In 2025, he signed the Executive Order on Eradicating Anti-Christian Bias, ensuring that Christian institutions and churches would be protected from state discrimination and legal harassment. This act demonstrated the continuing importance of rulers defending the faith, even in societies that claim to be religiously neutral. While the modern world lacks the overt religious conflicts of Charlemagne’s time, the principle remains: leaders have a duty to uphold and protect Christianity against forces that seek to undermine it.

Charles XII (1682-1718) of Sweden, known as Carolus Rex, ruled with a deep conviction that his kingship was a divine appointment to uphold biblical Christianity. He saw himself as a warrior for God, resisting both Catholic and Orthodox influences in the region, which he viewed as distortions of true Christianity. His military campaigns against Catholic Poland and Orthodox Russia were not merely political but also a defense of the Protestant faith. Like Charlemagne, he believed that Christian kings should actively protect doctrine rather than passively submit to clerical authorities.

The English Reformation is another example of this principle in action. Henry VIII’s break from Rome, while politically motivated, established the precedent that Christian rulers should not be subservient to the pope. Later, the Puritan and evangelical movements continued this tradition by emphasizing the biblical responsibility of leaders to uphold true doctrine. The rejection of papal overreach ensured that Christian rulers remained defenders of the faith rather than vassals of an ecclesiastical hierarchy.

Oliver Cromwell (1599-1658) led England as a Puritan ruler, ensuring that the nation adhered to biblical principles rather than papal corruption. As Lord Protector, Cromwell sought to reform England’s government and society according to Reformed Protestant values, purging Catholic and Anglican influences that he saw as remnants of idolatry and tyranny. Under his rule, England became a stronghold of Protestantism, with policies aimed at protecting religious liberty for Puritans while resisting Catholic encroachments. His leadership exemplified the role of a Christian statesman who saw government as an instrument to uphold divine truth rather than being subjugated to Rome’s influence.

William of Orange (1650-1702) played a pivotal role in defending Protestant England from Catholic absolutism, particularly during the Glorious Revolution of 1688. By deposing the Catholic King James II, William secured England as a Protestant nation, ensuring that the monarchy would remain aligned with biblical principles rather than subjugated to papal influence. His reign established the precedent that Christian rulers should actively protect their nations from the dangers of Catholic authoritarianism, securing both religious liberty and Protestant governance for future generations.

Frederick the Great of Prussia (1712-1786) was a defender of Protestant Christianity, resisting Catholic influence in his realm and ensuring that Prussia remained a Protestant stronghold in Europe. While he was known for his military prowess and administrative reforms, Frederick understood that a Protestant kingdom must not submit to Rome. He promoted religious toleration but ensured that Catholicism did not regain political dominance in Prussia. His reign demonstrated that rulers could uphold biblical Christianity while fostering a strong and independent nation, free from papal interference.

These historical examples reinforce the Council of Frankfurt’s key lesson: Christian rulers are accountable before God for preserving doctrinal purity and resisting theological corruption.

The Failure of Rome and Byzantium

By contrast, both Rome and Byzantium deviated from this model. The Eastern Roman (Byzantine) Empire fell into caesaropapism, where emperors dominated church doctrine, leading to unbiblical compromises such as the veneration of icons. The Roman Papacy, on the other hand, sought total supremacy over Christian rulers, enforcing corrupt doctrines and suppressing those who resisted.

The Council of Frankfurt stands as a rebuke to both systems. It demonstrated that Christian kings should defend the faith, not redefine it like the Byzantine emperors, nor submit to an unchecked ecclesiastical authority like the medieval popes.

This failure of Rome and Byzantium explains why God blessed the Protestant Reformation, which restored the proper role of rulers in defending biblical Christianity without being enslaved to papal decrees or Eastern superstitions. The Council of Frankfurt, led by Charlemagne, foreshadowed this restoration, setting the stage for later Protestant and evangelical triumphs.

Conclusion

The Council of Frankfurt was a defining moment in Christian governance, proving that rulers must be defenders of the faith rather than mere political figures. Charlemagne, following the example of biblical kings, protected true doctrine from icon veneration, Adoptionism, and papal interference. His leadership foreshadowed later Christian rulers such as Carolus Rex and Donald Trump, who recognized the divine mandate to uphold Christianity against corruption.

Charlemagne’s role at Frankfurt remains a model for future Christian leadership, demonstrating that rulers must uphold doctrinal purity and resist theological errors—whether they come from Rome, Byzantium, or modern secular powers. His legacy is a reminder that political neutrality is not an option in the defense of the gospel.