メルセン条約
After Charlemagne died in 814, the imperial crown passed to his son, Louis the Pious. Upon Louis' death in 840, it passed to his son Lothair, who was his co-ruler. By this point the territory of Charlemagne was divided into several territories ("cf". Treaty of Verdun, Treaty of Prüm, Treaty of Meerssen and Treaty of Ribemont), and over the course of the later ninth century the title of Emperor was disputed by the Carolingian rulers of Western Francia and Eastern Francia, with first the western king (Charles the Bald) and then the eastern (Charles the Fat), who briefly reunited the Empire, attaining the prize.