Initial charges of heresy were brought against Luther in the summer of 1518. The source for those charges is uncertain. One possibility was the rival Dominicans in Germany, led by John Tetzel, who was conferred a doctorate at the plenary chapter meeting of the Dominicans just prior to the legal proceedings against Luther, which essentially made him Luther’s equal as a doctor of the church and thus able to debate his critic. Another possibility was the Leipzig cleric Jerome Emser, a member of Duke George of Saxony’s court who interrogated Luther in July of that year. Yet another option was the letter of concern Albrecht of Mainz sent to Rome as a result of the opinion he received from his theology faculty after the publication of the 95 Theses. Whatever the source, Rome initiated proceedings in June on the basis of complaints made against Luther’s theology of indulgences and related criticism of papal authority.
The official response to Luther came from the pen of Sylvester Prierias, the master of the sacred palace in Rome and a noted theologian in his own right. Prierias composed an opinion against Luther that focused on his view of the papacy. For Prierias, the pope had authority over the church, he was infallible in matters of faith and morals, indulgences fell within the scope of faith and morals, therefore the pope had proper authority to institute indulgences. At roughly the same time as he received notice of the legal proceedings, Luther also received a copy of Prierias’ Dialogus, which explained in detail his criticisms of Luther’s position. Luther in turn had Prierias’ tract printed and then offered a rebuttal of his own, appealing not to papal authority, but Scriptural authority. In the process, he cited St. Paul, Augustine, and the fifteenth-century canonist, Nicholas Tudeschi (Panormitanus), in arguing that while popes can err, Scripture does not. Even though Luther had resisted making direct statements can the papacy, as he made clear in his later years, his opponents continued to shift the debate to questions of authority.
On the basis of Prierias’ opinion, Rome sent Luther a summons to appear for trial within sixty days, a letter he received on August 7, 1518. Though the summons indicated Luther had to stand trial in Rome, that requirement was relaxed. Cardinal Cajetan, the papal legate who presumably delivered the summons at Augsburg, was instructed to meet with Luther in person and give him an opportunity to recant. That meeting would take place in October of 1518.