While the recent restoration of the portals of the Rouen Cathedral invites us to rediscover an outstanding sculpture, this study proposes a renewed approach and comprehension keys to facilitate their “decryption”. Why does the library portal cover, at the end of the eighteenth century, almost 200 bas-reliefs featuring domesticated animals and hybrid creatures alongside the Creation of the World or Adam and Eve? How was this first Rouennese “model” taken up during the 14th century at the southern portal of Calende, but also at the primatiale Saint-Jean de Lyon, the Abbey Saint-Ouen de Rouen and even the Avignon Pope Palace? What artistic, religious and even political issues explain this success, which is both demanding (more than 860 bas-reliefs) and limited in time (end of XIVth century)? Opening up new perspectives in the field of iconographic analysis, the author carries out a genuine historical study: the prestige policy of major prefectures, the ‘storytelling’ of the images sculpted at the cathedral threshold, the culture of metamorphosis and the incredible inventiveness of the sculptors of the Middle Ages, the worship of the Holy at the heart of rivalries between sanctuaries, etc.