The shrine of Saint Heribert, bishop of Cologne, the base of the cross of Saint-Omer, or the many enamelled plaques scattered today across American and European museums all bear testimony to the emergence of the champlevé technique in the valleys of the Meuse and Rhine in the first half of the 12th century. 1 These objects, crafted in Mosan workshops or in ateliers of the Rhineland, in northern regions of present-day France or in England, exhibit a number of original and common traits. 2 To explain this phenomenon, early researchers – mostly Belgian specialists – invoked the extraordinary diffusion of so-called ‘Mosan’ art in the neighbouring regions, as well as in more distant territories, and its civilizing action within them. 3 Such an affirmation generated a heated debate, over time giving rise to reflections on more general questions such as the definition of style, the existence of regional and transregional schools of art, and the concepts of ‘influence’ and ‘transfer’. 4 This paper aims to offer a historiographical survey of the abundant literature brought about by this discussion, until the most recent period. 5