Meanwhile the Protestant princes refused to withdraw from the position they had taken up.
The emperor's letters to his ambassadors at Rome on the subject led to the discussion of the matter twice in the congregation of cardinals appointed especially for German affairs.
Although opinions differed, the pope wrote to the emperor that Charles could promise the convoking of a council with his consent, provided the Protestants returned to the obedience of the Church.
The Protestant rulers, meeting at Smalkald in December, 1535, rejected the proposed council.
In this they were supported by Kings Henry VIII and Francis I.
On 2 June, Paul III published the Bull calling all patriarchs, archbishops, bishops, and abbots to assemble at Mantua on 23 May, 1537, for a general council.
Cardinal legates were sent with an invitation to the council to the emperor, the King of the Romans, the King of France, while a number of other nuncios carried the invitation to the other Christian countries.
Owing to the feeling prevalent in Germany the demand was very dangerous.
Rome positively rejected the German national council, but did not absolutely object to holding a general council.
The nineteenth ecumenical council opened at Trent on 13 December, 1545, and closed there on 4 December, 1563.