 Alsace remained under Frankish control until the Frankish realm, following the Oaths of Strasbourg of 842, was formally dissolved in 843 at the Treaty of Verdun; the grandsons of Charlemagne divided the realm into three parts.Alsace formed part of the Middle Francia, which was ruled by the eldest grandson Lothar I. Lothar died early in 855 and his realm was divided into three parts.The part known as Lotharingia, or Lorraine, was given to Lothar's son.