The practice of diverting crusaders from one area of conflict to another can be traced back at least as far as the beginning of the twelfth century. Commuting of vows in this way was early recognized to be a papal prerogative and usually involved crusaders who had originally vowed to go to the Holy Land. In the twelfth century commutations occurred on only a few occasions, when steps were taken to divert crusaders to the Iberian Peninsula when it was under serious threat. Commutations became much more frequent in the first half of the thirteenth century and were used to provide manpower against Christians as well as infidels. At that time popes often took the initiative: Gregory IX was anxious to provide help for the Latin Empire of Constantinople and Innocent IV and his successors needed assistance against the Hohenstaufen. The papacy did not, however, coerce crusaders, and many refused to commute their vows. Criticism of commuting was voiced, although the redeeming of vows for money attracted greater opprobrium. Commuting became less common in the closing decades of the thirteenth century, but the reasons for this decline are not explained in the sources and can only be conjectured.