Lotharii Regnum
Just a few days before his death in late autumn of 855, Emperor Lothair I divided his realm of Middle Francia among his three sons, a partition known as Treaty of Prüm. Lothar II received the Middle Francia territory west of the Rhine stretching from the North Sea to the Jura mountains. It became known as "Regnum Lotharii" and early in the 10th century as Lotharingia or Lorraine (a designation subsequently applied only to the duchy of Lorraine). His elder brother Louis II received northern Italy and the title of Emperor, and his younger brother Charles received the western parts of his father's domains, Burgundy and the Provence.