The Protestants at first stipulated that it be held in Germany, while the pope insisted on an Italian venue. Mantua was chosen, but its duke refused; then Venice prevented a meeting at Vicenza. Finally Trent, an imperial city, almost in Italy, was selected as a compromise between the papal party and that of Holy Roman Emperor Charles V. There was an abortive start in 1542.
In 1544 the pope convened the council definitively. There were no Protestant delegates. The work of the council embraced dogmatic definition and correction of abuses, and it was so planned that discussion of doctrine and of reforms of practices could be carried on at the same time. The 10 years of delay bore good fruit, for the reformers arrived at the council intensively prepared in every question likely to be studied. The chief functions of the council were occasional solemn one-day sessions (25 in all, of which 10 dealt with formalities only) for the purpose of making the final decisions and declarations; the hard work of the council was done at informal, sometimes private, meetings. The council met at first in three great committees, later as a whole.
As with every ecumenical council since antiquity, the presence of the pope or his legates was required, and at Trent they drew up the agenda. The sessions of the council fell into three periods: 1–10 (1545–47), under Paul III; 11–16 (1551–52), under Julius III; and 17–25 (1562–63), under Pius IV. The two great interruptions were chiefly occasioned, first, by an impasse over the place of meeting after most of the bishops had left Trent for fear of the plague (1547), and, second, by the lack of interest of Paul IV (1555–59). Furthermore, the swiftly changing events of German politics often made delays seem wise. The numbers attending the council varied; in the first group of sessions there were less than 200, in the second group somewhat less, and in the third considerably more.