In the medieval cult of saints and relics, saints and items related to them were revered for their holiness and renowned for their miraculous powers. The vast varieties of relics gained such fame that over time that they developed a following that seems to the modern eye more related to the magical than to the religious. Boccaccio was well aware that this strong belief system could be turned to the advantage of crafty, skeptical men who profited from ingenuous superstition or, as in the case of Frate Cipolla (VI.10), are almost outwitted themselves.
The two novellas in which Boccaccio satirizes the cult of saints are I.1 and II.1. The first tells of Ser Cepperello who, despite his wicked life, is honored in death as a Saint. By implying that God works miracles through him, the author underscores the unpredictability of miraculous events. Similarly in II.1, the cathedral bells ring "of their own accord" at the death of a poor manual laborer named Arrigo, an event taken by the townspeople as proof of his saintliness. Martellino, having entered the crowd of worshippers disguised as a paralytic in order to approach the "saint," is attacked by the crowd. In tale's conclusion, however, Martellino and his companions go unpunished and even receive new clothes. The unfolding of events suggests an overturning of the lesson of the Decameron's initial novella and encourages the reader to see Arrigo's spontaneous canonization as false.
Popular faith in relics is addressed in VI.10 in which Frate Cipolla dupes the gullible Florentines with his "holy articles" and powerful rhetoric in exchange for their money. Although illiterate, they consider him as talented as Cicero himself, standing there with the "coals over which St. Lawrence was roasted."
This superstition in saints appears also when Panfilo tells that they pay an annual fee in the name of St. Anthony, for him to "protect [their] oxes, asses, pigs, and sheep from harm." Judging from similar customs mentioned by Dante (Paradiso 29.124ff.) and Masuccio Salernitano (tale 18 of his Novellino, ca. 1476), it would seem that this was an enduring object of satire.
Prayer also functions as a form of religious superstition. In II.2 Rinaldo d'Asti recites prayers in honor of St. Julian each morning for protection in his travels. Rinaldo's happy ending, after grave misfortune, is portrayed in Boccaccio's tale as possibly - though not unambiguously - the result of coincidental rather than actual belief in ritualistic prayer.
A comparable turn of events appears on the seventh day, that devoted to tricks. The first novella of this day features Monna Tessa, "of great intelligence and perspicacity," who convinces her husband to exorcise the "werewolf" outside their door with a "fine and godly prayer." In this episode, Boccaccio alludes to several magical/superstitious practices. Monna Tessa feigns fear of the werewolf, or fantasima, the legendary "animal resembling a satyr, or cat monkey, which goes around at night causing distress to people," and sets up an ass's skull on a stake. Though this had been an ancient rite to protect one's crops, Monna Tessa uses the skull to signal to her lover whether her husband is home. She also recites prayers against the werewolf with Gianni to communicate information to her lover, who is behind the door. To placate Gianni, she tells him that before going to bed she recited the Te lucis, a hymn attributed to St. Ambrose that was thought to invoke God's help against nocturnal spirits. The main prayer of this story, with which the couple "exorcises the werewolf," ridicules religious superstitions. The efficacy of this prayer (much like the prayer of Lady Matilde taught to Gianni by the laud-singers of Santa Maria Novella) is negated by Boccaccio's offhanded comments throughout.