In January 1519, at Altenburg in Saxony, the papal nuncio Karl von Miltitz adopted a more conciliatory approach. Luther made certain concessions to the Saxon, who was a relative of the Elector, and promised to remain silent if his opponents did. The theologian Johann Eck, however, was determined to expose Luther's doctrine in a public forum. In June and July 1519, he staged a disputation with Luther's colleague Andreas Karlstadt at Leipzig and invited Luther to speak. Luther's boldest assertion in the debate was that Matthew 16:18 does not confer on popes the exclusive right to interpret scripture, and that therefore neither popes nor church councils were infallible. For this, Eck branded Luther a new Jan Hus, referring to the Czech reformer and heretic burned at the stake in 1415. From that moment, he devoted himself to Luther's defeat.