Saints' lives are one of those sources least exploited by historians of fortresses. They may well, however, in their own way, provide information which it is difficult to find elsewhere. Of this immense literature, the works which probably most merit our attention are the Books of Miracles. Amongst their other admirable practices, saints were in the habit of delivering innocent prisoners, imprisoned, for the most part, in fortresses. Thus the story of their liberation and flight often involved the hagiographer in describing the disposition, of the site of the miracle of deliverance, that is, in describing, or at least suggesting, the location and the plan of the castle buildings, as well as enumerating the obstacles surmounted during the course of the escape. The information of a technical nature which can be garnered in this way cannot, of course, be accepted unquestioningly; hagiographical sources are, in fact, amongst the least reliable of those available to historians, and the traps they set are too well known to need emphasis here (uncertain dating of the stories, their constant rewriting, endless recourse to commonplaces drawn from models of the genre etc.). These faults are not, however, general and there exist works whose authors and dates of composition are precisely known; amongst them is the Book of Miracles of Sainte-Foy, which will be discussed here.

The Liber miraculorum sancte Fidis consists of two quite separate sections written by different authors.