Diet of Regensburg (1541)  The Colloquy of Regensburg, historically called the Colloquy of Ratisbon, was a conference held at Regensburg (Ratisbon) in Bavaria in 1541, during the Protestant Reformation, which marks the culmination of attempts to restore religious unity in the Holy Roman Empire by means of theological debate between the Protestants and the Catholics. Delegates from the various factions had met at Haguenau in 1540 and at Worms in January 1541 but the latter session of the Imperial Diet was adjourned by the Emperor Charles V as the Diet was preparing to meet at Regensburg. The subject for debate was to be the Augsburg Confession, the primary doctrinal statement of the Protestant movement, and the Apology of the Augsburg Confession, a defence of the Confession written by Philipp Melancthon. On 15 December 1540 a secret conference took place between Johann Gropper, canon of Cologne, and Gerhard Veltwick, the Imperial secretary, on the one side and Butzer and Capito, the delegates of Protestant Strasbourg, on the other. The two sides agreed their positions on original sin and justification, but the promise made by the Catholic party at Haguenau, to negotiate on the basis of the Confession and Apology, was withdrawn. Early in 1541, Butzer sent a draft of the conclusions to Joachim II, Elector of Brandenburg, with the request to communicate it to Luther and the other princes of the Protestant league. The document was essentially identical with the later so-called "Regensburg Book", which formed the basis of the Regensburg Conference in place of the Augsburg Confession. It was divided into twenty-three articles, some of which closely approached the Protestant view; but it decided no questions of dogma and did not exclude the Catholic positions. On 13 February 1541 the book reached the hands of Luther. In spite of the apparent concessions made in regard to the doctrine of justification, he perceived that the proposed articles of agreement could be accepted by neither party. On 23 February 1541 the Emperor entered Regensburg. In consideration of his difficult political situation, especially of the threatened war with the Ottoman Turks and the negotiations of the French king with the Protestants in his country, it was his desire to pacify Germany. The conference was opened on 5 April. The negotiators were Gropper, Pflug, and Eck on the Catholic side, under the oversight of the Papal Legate Cardinal Contarini; Bucer, the elder Johannes Pistorius, and Melanchthon for the Protestants.