How did Marsilius of Padua support Louis IV’s arguments against papal power?

Marsilius of Padua provided critical intellectual support for Louis IV’s resistance against papal authority through his influential treatise, Defensor pacis (“Defender of the Peace”). His arguments bolstered the emperor’s position in several key ways:1

• Subordination of the Church: Marsilius conceptualized the church as merely the Pars sacerdotalis (“priestly department”) of the state, arguing that the unity of the state must be preserved by strictly limiting the power of the church hierarchy.12
• Secular Sovereignty: Applying Aristotelian principles, he evolved a secular concept of the state where the primary responsibility is the maintenance of law, order, and tranquility. He asserted that the source of all political power and law is the people, who possess the right to choose their ruler, thereby challenging the necessity of papal confirmation for imperial legitimacy.12
• Ecclesiastical Governance: He concluded that the church’s supreme authority in matters of doctrine and morals should not rest with the pope, but with a general council representative of all believers, including both clergy and the laity.1

Marsilius actively assisted Louis IV during his Italian expedition, participating in the declaration of Pope John XXII as a heretic and the installation of an antipope, Nicholas V.1