Pope Innocent III was also a zealous protector of the Catholic faith and a strenuous opponent of heresy. His chief activity was turned against the Albigenses who had become so numerous and aggressive that they were no longer satisfied with just being adherents of heretical doctrines but even endeavoured to spread their heresy by force. They were especially numerous in a few cities of Northern and Southern France. During the first year of his pontificate, Innocent sent the two Cistercian monks Rainer and Guido to the Albigenses in France to preach to them the true doctrines of the Catholic faith and dispute with them on controverted topics of religion. The two Cistercian missionaries were soon followed by Diego, Bishop of Osma, then by Saint Dominic and the two papal legates. Peter of Castelnau and Raoul.