The Council opened on December 13, 1545, and continued its sittings (with interruptions) until December 4, 1563, the last being the twenty-fifth in number. The meetings of the Council took place at various times during the reigns of three Popes, Paul III., Julius III., and Pius IV., and amongst the enactments of the Council the Canon of Scripture, including the Apocrypha, was confirmed, and the Church named as its sole interpreter; that traditions were to be considered as equal with Scripture, and the seven sacraments of Baptism, Confirmation, the Lord's Supper, Penitence, extra-Unction, Orders, and Matrimony were also confirmed; transubstantiation, Purgatory indulgences, celibacy of the clergy, auricular confession, and other matters were dealt with.
The first sitting was held under Cardinal Del Monte, the papal legate, who rose amidst the assembled prelates and representatives and asked them whether it was their wish, "For the glory of God, the extirpation of heresy, and the reformation of the clergy and people, and the downfall of the enemy of the Christian name, to resolve and declare that the Sacred General Tridentine Council should begin and was begun?" The whole company, we are told, answered "Placet," a Te Deum was sung, and it was agreed that the first sitting of the Council should be held on the 7th of January. The sittings were continued at various times without any untoward event till the year 1552, when Maurice of Saxony invaded Tyrol, and although the Council was sitting, most of its members fled the country after having re-enacted the various decrees and ordinances which had been previously passed.
Ten years later, what was to all intents and purposes another Council met at Trent, and a solemn service was again held, at which Cardinal Gonzaga was elected president. A quarrel seems to have arisen between some of the archbishops and bishops and one of the French envoys. The former did not agree to some of the terms of the proposition made by the Archbishop of Reggio, whilst the latter raised an objection to the Council being considered a continuation of the first Council.
The building in which the Council sat has been stated at various times to have been the Cathedral, in the Piazza del Duomo, but there seems very little doubt now that the place of meeting was not there but in the Church of Santa Maria Maggiore, situated on the Piazza of the same name. In it on the north wall of the Choir hangs a large picture representing some three hundred of the various chief dignitaries as they sat in the Council Chamber. The members numbered nearly a thousand in all, and in addition to the cardinals, archbishops, bishops, abbots, chiefs of religious orders, and representatives from the University, there were also present ambassadors from the Emperor of Germany, and from the Kings of France, Spain, and Portugal, from the republic of Venice and Genoa, from Switzerland, and from the German electors.