Roer is the name of a département of the First French Empire in present day Germany and the Netherlands. It was named after the river Rur, which flows through the département. It was formed in 1795, when the Southern Netherlands and the left bank of the Rhine were occupied by the French. The département de la Roer was formed from the duchies of Jülich and Cleves, the part of the Archbishopric of Cologne left of the Rhine, the free city of Aachen, the Prussian part of the duchy of Guelders and some smaller territories.