ORTNAU or ORTENAU, a district or canton in Germany, in Suabia, lying along the Rhine opposite Strasburg. It included eight or ten small towns, of which Offenburg, Gegensbach, and Zell, were the most considerable: these towns formed a small federation, and held immediately of the empire. At the distribution of the indemnities, after the peace of Luneville, this territory, with the Brisgau, was assigned to the duke of Modena; but the greater part of it was afterwards annexed to the grand duchy of Baden.