In 1234, Pope Gregory IX (1227-1241) called for a crusade to exterminate heretics in Bosnia, a call that he would repeat in 1238. In this chapter, I argue that the Bosnian crusade(s) of the 1230s was/were launched not against the adherents of a particular doctrine but against a place, one which was thought to be an especial incubator of heretical pestilence and a dire threat to this transformative project. This is why I contend also that it is productive to situate the crusade under the same umbrella as preaching and the construction of churches; that is, as acts also designed to secure the salvation of Christendom via invasive alteration of the imaginative and physical landscape of Bosnia. We do not see a cautious adaptation under Gregory to Bosnian culture and society but an attempt to secure its obedience to the Latin Church via an influx of friars and Hungarians and the transformation of its people from Bosnians into either crucesignati or heretics.