As soon as he heard of the murder, the Pope ordered the legates to preach a crusade against the Cathars, and wrote a letter to Philip Augustus, King of France, appealing for his intervention—or an intervention led by his son, Louis. This was not the first appeal, but some see the murder of the legate as a turning point in papal policy. The chronicler of the crusade which followed, Peter of Vaux de Cernay, portrays the sequence of events in such a way that, having failed in his effort to peaceably demonstrate the errors of Catharism, the Pope then called a formal crusade, appointing a series of leaders to head the assault.