Knowledge about the early development of champlevé is uncertain. It figured in the Celtic art of western Europe in the Roman period and beyond. Centring in the Rhine River valley around Cologne and in Belgium's Meuse River valley, champlevé production flourished especially during the late 11th and 12th centuries. Among the finest and best-known work was that of the Mosan school centred at the Benedictine abbey of Stavelot near Liège, now in Belgium. Among the period's most famous enamelers were Nicholas Of Verdun, who flourished in Cologne from the second half of the 12th century to the early 13th century, and Godefroid de Claire, who was largely active at Stavelot from around 1130 to 1150. See also Mosan school.