Having original written documenta and maps from the Service Historique de l'Armée de Terre (Château de Vincennes near Paris, France) as his starting point, the author deals with diplomatic procedure and technical carrying out of the delimitation between Napoleon's French and the Austrian Empires through a part of the Slovenian ethnical territory. Generally, it followed the old frontier line between the Hapsburg duchies of Carinola and Styria, but changed it in some areas, esp. around the borough of Motnik. The new state boundary resulted from the work of two bilateral commissions, chaired respectively by Generals A.C. Guilleminot and A. Zach in 1809/1810 as well as Baron M.J.R. de Lort and Count J. Klobusiczky in spring of 1811. The paper gives a detailed description of the boundary, which is completed by several reproductions of original maps executed upon the two commissions' request. After the fall of the French Illyria in autumn of 1813, the established state boundary served for another century, until 1918, as the administrative frontier of two Austrian Länder, the duchies of Styria and Corniola. Some subsequent 20th century administrative boundaries linked up to it as well.