 According to three 13th @-@ century authors ( Matthew Paris , <unk> di Adam and Bernard of <unk> ) , John became a Franciscan friar before his death . They agree that John 's declining health contributed to his conversion , but Bernard also described a recurring vision of an old man urging the emperor to join the Franciscans . Most 13th @-@ century sources suggest that John died between 19 and 23 March 1237 , the only Latin emperor to die in Constantinople . 
