There was frequent interchange between Swiss and German Protestants early in the Reformation, and Bucer's Strasbourg had some Reformed characteristics, but Germany remained firmly Lutheran and anti-Calvinist through 1560. Following the death of Lutheran Wittenberg reformer Philipp Melanchthon in 1560, Frederick III, Elector Palatine began to promote the Reformed faith in his own realm. He invited two students of Calvin, Zacharias Ursinus and Kaspar Olevianus, to the university city of Heidelberg in 1561. The two men co-operated in writing the Heidelberg Catechism in 1563 to replace the conflicting catechisms currently circulating in the realm. Despite opposition from the Holy Roman Emperor and other German princes, Frederick continued to institute Reformed worship in the Palatinate. In 1566 he was called to appear at the Diet of Augsburg to account for his violation of the Treaty of Augsburg. His testimony was so impressive that no action was taken against him, leaving the Palatinate free to continue in a Reformed direction. Frederick died in 1576 and was succeeded by his son Louis VI, who was not friendly to the Reformed faith. 600 Reformed professors and ministers were expelled. These refugees scattered to various cities. In 1583, John Casimir restored the Reformed faith in the Palatinate, and this policy was continued by his successor Frederick IV. Some other German states and cities also adopted the Heidelberg Catechism and the Reformed faith.