On the death of Julius III. (1555) Marcellus II. succeeded, but his reign was cut short by death (22 days). In the conclave that followed Cardinal Pietro Caraffa, the first general and in a certain sense the founder of the Theatines, received the required majority of votes notwithstanding the express veto of the Emperor. He was proclaimed Pope under the title of Paul IV.[3] (1555-9). During his life as an ecclesiastic the new Pope had been remarkable for his rigid views, his ascetic life, and his adherence to Scholastic as opposed to Humanist views. As nuncio in Spain he had acquired a complete distrust of the Spanish rulers, nor was this bad impression likely to be removed by the treatment he received from the Austro-Spanish party when appointed Archbishop of Naples. The conclusion of the religious peace of Augsburg (1555) and the proclamation of Ferdinand I. were not calculated to win the sympathy of Paul IV. for the House of Habsburg. Hence, he put himself in communication with the Italian opponents of Philip II. of Spain, and concluded an alliance with France. The French army despatched to Naples under the leadership of the Duke of Guise was out-manoeuvred completely by the Spanish Viceroy, the Duke of Alva, who followed up his success by invading the Papal States and compelling the Pope to sue for peace (1556). The unfriendly relations existing between Paul IV. and Philip II. of Spain, the husband of Queen Mary I., rendered difficult the work of effecting a complete reconciliation between England and the Holy See. Owing to the disturbed condition of Europe and the attitude of the Emperor and the King of Spain, it would have been impossible for the Pope even had he been anxious to do so to re-convoke the council. He would not so much as consider the idea of selecting Trent or any German city as a fit place for such an assembly, while the Austro-Spanish rulers were equally strong against Rome or any other place in Italy. But of his own initiative Paul IV. took strong measures to reform the Roman Curia, established a special commission in Rome to assist him in this work, stamped out by vigorous action heretical opinions that began to manifest themselves in Italy, and presided frequently himself at meetings of the Inquisition. He even went so far as to arrest Cardinal Morone on a suspicion of heresy, and to summon Cardinal Pole to appear before the tribunal of the Inquisition. By the Romans he had been beloved at first on account of his economic administration whereby the taxes were reduced considerably, but the disastrous results of the war against Philip II. in Naples effaced the memory of the benefits he had conferred, and he died detested by the people. After his death the city was at the mercy of the mob, who plundered and robbed wholesale for close on a fortnight before order could be restored.
In the conclave that followed the two great parties among the cardinals were the French and the Austro-Spanish, neither of which, however, was strong enough to procure the election of its nominee. After a struggle lasting three months Cardinal Giovanni Angelo de' Medici, who was more or less neutral, was elected by acclamation. He was proclaimed under the title of Pius IV. (1559-65). The new Pope had nothing of the stern morose temperament of his predecessor. He was of a mild disposition, something of a scholar himself, inclined to act as a patron towards literature and art, and anxious to forward the interests of religion by kindness rather than by severity. He was determined to proceed with the work of the council at all costs, and as a first step in that direction he devoted all his energies to the establishment of friendly relations with the Emperor Ferdinand I. and with Spain. In all his schemes for reform he was supported loyally by his nephew, Charles Borromeo, whom he created cardinal, and to whom he entrusted the work of preparing the measures that should be submitted to the future council.
When all arrangements had been made the Bull of re-convocation, summoning the bishops to meet at Trent at Easter 1561, was published in November 1560. Though not expressly stated in the document, yet it was implied clearly enough that the assembly was not to be a new council but only the continuation of the Council of Trent. This was not satisfactory to France, which demanded a revision of some of the decrees passed at Trent, and which objected strongly to the selection of Trent as the meeting-place. The Emperor Ferdinand I. and Philip II. expressed their anxiety to further the project of the Pope. Delegates were sent from Rome to interview the Lutheran princes and theologians, but only to meet everywhere with sharp rebuffs. In an assembly held at Naumburg in 1561 the Lutherans refused to attend the council, unless they were admitted on their own terms, while many of the Catholic princes and bishops showed no enthusiasm to respond to the papal convocation. When the legates arrived to open the council they found so few bishops in attendance that nothing could be done except to prepare the subjects that should be submitted for discussion.