Jean Wirth is Professor of Middle Ages history of art at the University of Geneva. Overshadowing the evolution of the centre-peripheral relationship in the figurative decor of the medieval church, it appears that the elements articulated in these terms are remarkably unstable in the diachrony and even in the synchrony. This is due to ambivalence towards the fence, seductions of the world and ultimately the sacred itself. From a methodological point of view, this instability is unparalleled...