Mersen, Treaty of, 870, redivision of the Carolingian empire by the sons of Louis I, Charles the Bald (later Charles II) of the West Franks (France) and Louis the German of the East Franks (Germany), signed at Mersen (Dutch Meersen), now in the Netherlands. The treaty superseded the tripartite division of the empire in 843 (see Verdun, Treaty of). It divided the kingdom of Lotharingia between Charles and Louis, following the death (869) of their nephew, Lothair, king of Lotharingia. France obtained the territories roughly corresponding to the modern Netherlands, Belgium, and Lorraine and Germany received Alsace and the left bank of the Lower Rhine. The borders established did not last long.