A movement set off by the Catholic Church to curtail the spread of Protestantism that was threatening its power. Though the official launching of the Counter-Reformation took place at the Council of Trent, convoked in 1545 by Pope Paul III, steps had already been taken to fight Protestantism. In 1540, Paul confirmed the Jesuit Order, its main purpose to convert the heathen through missionary work. Two years later, he established the Inquisition to extirpate heretics from the Catholic world and the Index of Forbidden Books to prevent the propagation of dissenting ideas. New dioceses were established in regions where Protestantism was considered a threat and seminaries opened so clerics could be trained to fight hereticism effectively.
The Counter-Reformation affected art as well. A vast number of churches were erected, many following the prescriptions of St. Charles Borromeo, one of the guiding forces of the Council of Trent who, in 1577, wrote a treatise on the building of these structures. Gabriele Paleotti, archbishop of Bologna, wrote the Intorno alle imagini in 1582, a guide on the proper depiction of sacred and profane images, as specified by the Tridentine council. These types of texts served to propagate the guidelines for Baroque art: clarity of representation, historical accuracy, emphasis on emotional content to invoke piety, and narratives that assert the validity of Catholic doctrines, particularly those questioned by the Protestants.
Historical dictionary of Renaissance art. Lilian H. Zirpolo. 2008.