Pius IV

Pius IV inherited a council that had already run, in fits and starts, for nearly two decades by the time of his election in 1559. Trent had opened under Paul III in 1545, been suspended more than once amid war and plague, and by the late 1550s its eventual completion was no longer something the church could take for granted. Pius IV reconvened it for its third and final period in 1562, and it was under his authority that the council finished its work and closed in December 1563.

He confirmed the council's decrees the following year, in 1564, giving them formal papal authority rather than leaving them as the acts of an assembly. That single administrative act is why Trent's decisions became binding Catholic doctrine and discipline rather than remaining a set of proposals, and it is the reason his pontificate is remembered less for any personal theological program than for successfully closing a process three previous popes had failed to finish.

Much of the practical administration of turning Trent's decrees into functioning church policy fell to his nephew, Charles Borromeo, whom he had created cardinal and who is generally credited with the energy behind the reforms that followed, while Pius IV himself supplied the papal authority that made those reforms binding.

In the same year he confirmed Trent's decrees, 1564, Pius IV promulgated two documents that shaped Catholic practice for centuries afterward. The Index of Prohibited Books, drawn up at the council, listed works Catholics were forbidden to read or possess, formalizing a mechanism of censorship the church had used informally for decades into a standing institutional apparatus that would continue, revised repeatedly, into the twentieth century.

The Tridentine Profession of Faith, promulgated the same year, was an oath of orthodoxy required of bishops, beneficed clergy, university teachers and converts received into the Roman church, a practical enforcement mechanism that made adherence to Trent's doctrinal conclusions a condition of holding office or teaching rather than a matter of private belief. Pius IV is credited with enacting these texts rather than authoring their content, since both were substantially the council's own work; his role was to give them the force that only papal promulgation could supply.

Together the two documents illustrate how Trent's authority reached the church's daily life: not only through doctrine defined in council sessions, but through an index that controlled what could be read and an oath that controlled who could teach, both dated to the final year of Pius IV's central achievement.