The Legate Giacopo returned to Hungary satisfied that the land was converted, but success proved fleeting. Either Ninoslav’s conversion was feigned or he was unable to control his heretic subjects, for in the next year, 1234, we find Gregory complaining that heresy was increasing and rendering Bosnia a desert of the faith, a nest of dragons and a home of ostriches. In conjunction with Andreas he ordered a crusade, and Coloman was instructed to attack the heretics. The Carthusian Prior of St. Bartholomew was sent thither to preach it with Holy Land indulgences, and by the end of 1234 Coloman laid Bosnia waste with fire and sword. Ninoslav threw himself heart and soul with the Cathari, and the struggle was bloody and prolonged. The Legate Giacopo induced Bela IV. to take an oath to extirpate all heretics from every land under his jurisdiction, and the Franciscans hastened to take a hand in the good work. They commenced with the city of Zara, but the Archbishop of Zara, instead of seconding their labors, impeded them, which earned for him the emphatic rebuke of Gregory. Indeed, from the account which Yvo of Narbonne gives about this time of the Cathari of the maritime districts, they could not have been much disturbed by these proceedings.[329]
In 1235 the crusaders were unlucky. Bishop John lost all hope of recovering his see and asked Gregory to relieve him of it, as the labors of war were too severe for him; but Gregory reproved his faintheartedness, telling him that if he disliked war the love of God should urge him on.[330] In 1236 the aspect of affairs improved, probably because Bela IV. had replaced Andreas on the throne of Hungary, and because the crusaders were energetically aided by Sebislav, Duke of Usora, the son of the former Ban Stephen, who hoped to recover the succession. He was rewarded by Gregory calling him a lily among thorns and the sole representative of orthodoxy among the Bosnian chiefs, who were all heretics. At last, in 1237, Coloman triumphed, but heresy was not eradicated, in spite of his efforts through the following years. In fulfilment of his request, Gregory ordered the consecration of the Dominican Ponsa as Bishop of Bosnia, and soon afterwards appointed Ponsa as legate for three years in order that he might exterminate the remnant of heresy. It must have been a tolerably large remnant, for in the same breath he promised the protection of the Holy See to all who would take the cross to extirpate it. In 1239 the Provincial Prior of Hungary was ordered to send to the heretic districts a number of friars, powerful in speech and action, to consummate the work. Ponsa, though bishop and legate, had no revenues and no resources, so Gregory ordered paid over to him the moneys collected from crusaders in redemption of vows, and the sum which Ninoslav, during his interval of orthodoxy, had given to found a cathedral. By the end of 1239 heresy seemed to be exterminated, but scarce had Coloman and his crusaders left the land when his work was undone and heresy was as vigorous as ever. In 1240 Ninoslav appears again as Ban, visiting Ragusa with a splendid retinue to renew the old treaty of trade and alliance. King Bela’s energies, in fact, were just then turned in another direction, for Assan, the Bulgarian prince, had declared in favor of the Greeks; his people therefore were denounced as heretics and schismatics, and Bela was stimulated to undertake a crusade against him, for which, as usual, Holy Land indulgences were promised. It was hard to make head at once against so many enemies of the faith, and in the confusion the Cathari of Bosnia had a respite. Still more important for them as a preventive of persecution was the Tartar invasion which, in 1241, reduced Hungary to a desert. In the bloody day of Flusse Sajo the Hungarian army was destroyed, Bela barely escaped with his life, and Coloman was slain. The respite was but temporary, however, for in 1244 Bela again overran Bosnia. Ninoslav made his peace and the heretics were persecuted, until 1246, when Hungary was involved in war with Austria, and promptly they rose again with Ninoslav at their head.[331]