Despite the defeat of the conciliar party at Basel when emperor Frederick III signed the 1448 Concordat of Vienna that affirmed his support of the papacy, calls for a council to reform the church “in head and members”-beginning with the pope and working its way down through the entire ecclesiastical hierarchy-remained prevalent. Appeals for a council to address certain grievances, or Gravamina, from the German nation demanded the reform of Rome and less interference in the churches of the Empire. Many popes were resistant. One reason was the 1460 papal bull Execrabilis, promulgated by Pius II, which declared attempts to appeal a decision of the pope to a general council heretical and subject to excommunication. Another reason was the concern on the part of many popes that a new council might resuscitate the more extreme opinions of the conciliar movement, such as conciliar superiority to the pope or the right to convoke a council independent of papal participation. Though numerous popes were elected on the condition that they would convoke a general council, the only one convened between the Council of Basel and Trent was Lateran V and was itself a response to an alternative council (conciliabalum, or pseudo-council) that the papacy deemed seditious. The results of Lateran V did little to address the larger problems facing the church, in particular the proliferation of pluralism, absenteeism, simony, and the lack of rigorous moral or theological standards for the priesthood.
The controversy over Luther’s theology intensified cries for a council. Luther himself called for one at several junctures in his career. In the wake of the 1521 Edict of Worms condemning Luther’s teaching, the German princes demanded a “free Christian council on German lands” to rule on the matter ecclesiastically rather than politically. The death of Leo X in 1521 and accession of Adrian VI—a Dutchman and the last pope from outside of Italy until the twentieth century—to the papal see gave hope, but his untimely death the next year stinted it. Clement VII succeeded him and due to his conflict with Charles V repeatedly dodged the emperor’s requests for a council. Finally, the newly elected Paul III in 1534 established a committee to put together reform proposals for consideration at the council and in 1536 published a bull convoking the council in Mantua for the next year. Ongoing war between France and the Empire caused Paul III to suspend the convocation and propose an alternative location on Italian soil. The council was convoked again in 1543, to be held in Trent, though it was also suspended until the 1544 Peace of Crépy between the Empire and France enabled French support for the council.
The Council of Trent officially opened in December of 1545 and took place in three separate sessions. Each session was to address alternately doctrinal and disciplinary concerns, but this did not bear out. The first session (1545-47), composed of only 31 bishops, dealt strictly with theological matters and rejected several Protestant positions through its decrees on the relationship between Scripture and tradition and the doctrine of justification. The second session (1553-55) like the first failed to address pressing ecclesiastical matters and instead focused on theology, this time rejecting the Protestant definition of original sin. The third and final session (1561-63) was the most extensive. It included 255 bishops from throughout the church and led to the most comprehensive conciliar reforms since Lateran IV. It discouraged (without necessarily prohibiting) pluralism, proscribed absenteeism by defining the residency of bishops as a divine institution, encouraged episcopal visitation and preaching in the local diocese, established a pattern for regular convocation of diocesan and regional synods, and finally chartered the formation of diocesan seminaries for the training of priests.