The General Council of Trent, 1545-63 A.D. 

The Council of Trent, held in Trento, northern Italy, took place in 3 periods over 18 years (1545-1563) and was the 19th ecumenical council of the Catholic Church. It was convened primarily to address the challenges posed by the Protestant Reformation, in particular the teachings of Martin Luther and to clarify and codify Catholic doctrine (e.g. scripture & tradition, original sin and justification, the sacraments, veneration of the saints, and condemnation of heresies, etc.).

The General Council of Trent, 1545-63 A.D. - Papal Encyclicals