On 28 November, 1518, Luther had appealed from the pope to a general council because he was convinced that he would be condemned at Rome for his heretical doctrines. The Diet held at Nuremberg in 1523 demanded a "free Christian council" on German soil, and at the Diet held in the same city in 1524 a demand was made for a German national council to regulate temporarily the questions in dispute, and for a general council to settle definitely the accusations against Rome, and the religious disputes. Owing to the feeling prevalent in Germany the demand was very dangerous. Rome positively rejected the German national council, but did not absolutely object to holding a general council. Emperor Charles V forbade the national council, but notified Clement VII through his ambassadors that he considered the calling of a general council expedient and proposed the city of Trent as the place of assembly. In the years directly succeeding this, the unfortunate dispute between emperor and pope prevented any further negotiations concerning a council. Nothing was done until 1529 when the papal ambassador, Pico della Mirandola, declared at the Diet of Speyer that the pope was ready to aid the Germans in the struggle against the Turks, to urge the restoration of peace among Christian rulers, and to convoke a general council to meet the following summer. Charles and Clement VII met at Bologna in 1530, and the pope agreed to call a council, if necessary. The cardinal legate, Lorenzo Campeggio, opposed a council, convinced that the Protestants were not honest in demanding it. Still the Catholic princes of Germany, especially the dukes of Bavaria, favoured a council as the best means of overcoming the evils from which the Church was suffering; Charles never wavered in his determination to have the council held as soon as there was a period of general peace in Christendom.

The matter was also discussed at the Diet of Augsburg in 1530, when Campegio again opposed a council, while the emperor declared himself in favour of one provided the Protestants were willing to restore earlier conditions until the decision of the council. Charles's proposition met the approval of the Catholic princes, who, however, wished the assembly to meet in Germany. The emperor's letters to his ambassadors at Rome on the subject led to the discussion of the matter twice in the congregation of cardinals appointed especially for German affairs. Although opinions differed, the pope wrote to the emperor that Charles could promise the convoking of a council with his consent, provided the Protestants returned to the obedience of the Church. He proposed an Italian city, preferably Rome, as the place of assembly. The emperor, however, distrusted the pope, believing that Clement did not really desire a council. Meantime, the Protestant princes did not agree to abandon their doctrines. Clement constantly raised difficulties in regard to a council, although Charles, in accord with most of the cardinals, especially Farnese, del Monte, and Canisio, repeatedly urged upon him the calling of one as the sole means of composing the religious disputes. Meanwhile the Protestant princes refused to withdraw from the position they had taken up. Francis I, of France, sought to frustrate the convoking of the council by making impossible conditions. It was mainly his fault that the council was not held during the reign of Clement VII, for on 28 Nov., 1531, it had been unanimously agreed in a consistory that a council should be called. At Bologna in 1532, the emperor and the pope discussed the question of a council again and decided that it should meet as soon as the approval of all Christian princes had been obtained for the plan. Suitable Briefs addressed to the rulers were drawn up and legates were commissioned to go to Germany, France, and England. The answer of the French king was unsatisfactory. Both he and Henry VIII of England avoided a definitive reply, and the German Protestants rejected the conditions proposed by the pope.

The next pope, Paul III (1534-49), as Cardinal Alessandro Farnese, had always strongly favoured the convening of a council, and had, during the conclave, urged the calling of one. When, after his election, he first met the cardinals, 17 October, 1534, he spoke of the necessity of a general council, and repeated this opinion at the first consistory (13 November). He summoned distinguished prelates to Rome to discuss the matter with them. Representatives of Charles V and Ferdinand I also laboured to hasten the council. The majority of the cardinals, however, opposed the immediate calling of a council, and it was resolved to notify the princes of the papal decision to hold a church assembly. Nuncios were sent for this purpose to France, Spain, and the German king, Ferdinand. Vergerio, nuncio to Ferdinand, was also to apprise the German electors and the most distinguished of the remaining ruling princes personally of the impending proclamation of the council. He executed his commission with zeal, although he frequently met with reserve and distrust. The selection of the place of meeting was a source of much difficulty, as Rome insisted that the council should meet in an Italian city. The Protestant rulers, meeting at Smalkald in December, 1535, rejected the proposed council. In this they were supported by Kings Henry VIII and Francis I. At the same time the latter sent assurances to Rome that he considered the council as very serviceable for the extermination of heresy, carrying on, as regards the holding of a council, the double intrigue he always pursued in reference to German Protestantism. The visit of Charles V to Rome in 1536 led to a complete agreement between him and the pope concerning the council. On 2 June, Paul III published the Bull calling all patriarchs, archbishops, bishops, and abbots to assemble at Mantua on 23 May, 1537, for a general council. Cardinal legates were sent with an invitation to the council to the emperor, the King of the Romans, the King of France, while a number of other nuncios carried the invitation to the other Christian countries. The Netherlander Peter van der Vorst was sent to Germany to persuade the German ruling princes to take part. The Protestant rulers received the ambassador most ungraciously; at Smalkald they refused the invitation curtly, although in 1530 they had demanded a council. Francis I took advantage of the war that had broken out between himself and Charles in 1536 to declare the journey of the French bishops to the council impossible.

Meanwhile preparations were carried on with zeal at Rome. The commission of reform, appointed in July, 1536, drew up a report as the basis for the correction of the abuses in ecclesiastical life; the pope began preparations for the journey to Mantua. The Duke of Mantua now raised objections against the holding of the assembly in his city and made conditions which it was not possible to accept at Rome. The opening of the council, therefore, was put off to 1 November; later it was decided to open it at Vicenza on 1 May, 1538. The course of affairs, however, was continually obstructed by Francis I. Nevertheless the legates who were to preside at the council went to Vicenza. Only six bishops were present. The French king and the pope met at Nice, and it was decided to prorogue until Easter, 1539. Soon after this the emperor also desired to postpone the council, as he hoped to restore religious unity in Germany by conferences with the Protestants. After further unsuccessful negotiations both with Charles V and Francis I the council was indefinitely prorogued at the consistory of 21 May, 1539, to reassemble at the pope's discretion. When Paul III and Charles V met at Lucca in September, 1541, the former again raised the question of the council. The emperor now consented that it should meet at Vicenza, but Venice would not agree, whereupon the emperor proposed Trent, and later Cardinal Contarini suggested Mantua, but nothing was decided. The emperor and Francis I were invited later to send the cardinals of their countries to Rome, so that the question of the council could be discussed by the college of cardinals. Morone worked in Germany as legate for the council, and the pope agreed to hold it at Trent. After further consultations at Rome, Paul III convoked on 22 May, 1542, an ecuмenical council to meet at Trent on 1 Nov. of the same year. The Protestants made violent attacks on the council, and Francis I opposed it energetically, not even permitting the Bull of convocation to be published in his kingdom.

The German Catholic princes and King Sigismund of Poland consented to the convocation. Charles V, enraged at the neutral position of the pope in the war that was threatening between himself and Francis I, as well as with the wording of the Bull, wrote a reproachful letter to Paul III. Nevertheless, preparations were made for the council at Trent, by special papal commissioners, and three cardinals were appointed later as conciliary legates. The conduct, however, of Francis I and of the emperor again prevented the opening of the council. A few Italian and German bishops appeared at Trent. The pope went to Bologna in March 1543, and to a conference with Charles V at Busseto in June, yet matters were not advanced. The strained relations which appeared anew between pope and emperor, and the war between Charles V and Francis I, led to another prorogation (6 July, 1543). After the Peace of Crespy (17 Sept., 1544) a reconciliation was effected between Paul III and Charles V. Francis I had abandoned his opposition and declared himself in favour of Trent as the place of meeting, as did the emperor. On 19 Nov., 1544, the Bull "Laetare Hierusalem" was issued, by which the council was again convoked to meet at Trent on 15 March, 1545. Cardinals Giovanni del Monte, Marcello Cervini, and Reginald Pole were appointed in February, 1545, as the papal legates to preside at the council. As in March only a few bishops had come to Trent, the date of opening had to be deferred again. The emperor, however, desired a speedy opening, consequently 13 December, 1545, was appointed as the date of the first formal session. This was held in the choir of the cathedral of Trent after the first president of the council, Cardinal del Monte, had celebrated the Mass of the Holy Ghost. When the Bull of convocation and the Bull appointing the conciliary legates were read, Cardinal del Monte declared the ecuмenical council opened, and appointed 7 January as the date of the second session. Besides the three presiding legates there were present: Cardinal Madruzzi, Bishop of Trent, four archbishops, twenty-one bishops, five generals of orders. The council was attended, in addition, by the legates of the King of Germany, Ferdinand, and by forty-two theologians, and nine canonists, who had been summoned as consultors.

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