Luther was still within the limits of orthodox sentiment and practice, and the protection of the Elector embarrassed the Pope. A more diplomatic envoy, Karl von Militz, a Papal chamberlain, was sent to Germany, and some months were spent in amiable correspondence. Luther promised to be silent if his opponents would keep silence, and wrote a respectful letter to the Pope; to which Leo made a gracious reply. But the truce was little more than a diplomatic regard for Papal interests during the period of the imperial election, and the policy of silence soon proved impossible for both sides. Ulrich von Hutten and other critics encouraged Luther to assail the Papal authority, and the exaggerations of his opponents reacted on the growth of his mind. By the end of 1519 he seems to have concluded, with some firmness, that the Papal system was an unwarranted addition to primitive Christianity, and a formidable movement supported his ideas. In January (1520) Luther's case was submitted to a commission of theologians at Rome, and the Elector was summoned to compel him to retract. Frederic refused, and in June Leo signed the Bull _Exsurge Domine_; Luther was to be excommunicated if he did not submit within sixty days, and the secular authorities would incur an interdict if they did not surrender him. It is not of material interest to quarrel with the Pope's procedure: to point out that the disappointed Cajetan was one of the heads of the commission of inquiry, and that Luther's vehement opponent Eck was one of the two legates entrusted with the publication of the Bull. Rome demanded submission; and, if Luther had submitted, some other German would before long have instituted the Reformation. Europe was ripe for schism, and it may be doubted whether even a reform of the Church would have long prevented the growth of a body of men holding the Reformers' view of the bases of Papal authority. On December 10th (1520) Luther publicly burned the Bull. Even this act was not without orthodox precedent, but Luther was constantly advancing. He was summoned before the Diet of Worms in April (1521), and he then stated that the word of neither Popes nor Councils would condemn him; he must be judged by reason and Scripture. But the political situation, which casts its shadow throughout on the development, was now modified. Charles obtained his wish of an alliance with the Papacy against France. This alliance was signed on May 8th: on the 12th the Diet issued the Edict of Worms. Luther was, in accordance with the Pope's second Bull,[300] declared a heretic. He retreated to the Wartburg under the protection of Frederic, and the gravest phase of the struggle opened.[301]