Transjurania originally was a duchy of the Carolingian Empire, covering the Central Plateau from the Jura Mountains up to the Great St Bernard Pass in the Western Alps. It thereby roughly corresponded to western Switzerland, i.e. the parts west of the Brünig-Napf-Reuss line, including the Romandy with the cities of Geneva, Lausanne and Sion, as well as the cantons of Aargau, Berne and Valais and adjacent parts of the French départements Haute-Savoie and Ain, as well as the Aosta Valley which today belongs to Italy. Together with the Burgundian comital estates around Besançon and Dole on the Doubs river northwest of the Jura range, the Transjurane territories became part of the short-lived Middle Frankish realm of Emperor Lothair I upon the 843 partition by the Treaty of Verdun.