The so-called "mayors", ruling in the name of the kings, gained more power now and knew exactly how to use it to their own advantage. One of the most powerful of such families were the Pippins. When, in 751 AD, the pope was threatened by the Langobards (Lombards), Pippin (Pépin) III came to his aid and was rewarded by being crowned "King of the Franks".
The empire of his son Charles the Great (Charlemagne) spread from the Pyrenees to the Danube, and from Friesland to the middle of Italy. Charlemagne was crowned "Roman Emperor" in 800 AD. In economic and cultural terms the basins of the Meuse and the Rhine were the centre of his empire. The administrative language of the Frankish empire was still Latin, but in the vernacular Old French took over from Gallo-Roman. Latin became unintelligible to the Romance-speaking population (because of the restoration of classical Latin: see also the section on the influence of Latin and French on Middle Dutch)
This also formed the end of multilingualism in the area between the Seine and the Rhine. A language boundary running from west to east now separated the two monolingual areas with Germanic in the north and Romance in the south. Charlemagne's son Louis the Pious followed him to the throne in 814 AD, and immediately found problems with the administration of this great empire. As a solution he chose to introduce the feudal system, but the heritability of tenure also took power away from the king.

In the Treaty of Verdun (843 AD) Louis's empire was split between his sons. Lothair I received the title of emperor, the Italian possessions and the area between the Scheldt, Meuse, Saône, Rhône and Rhine, which was known as Middle Francia. Charles the Bald was granted the area of West Francia, and the third brother Louis the German gained East Francia. Lothair died in 855 AD and his empire in turn was also divided into three parts, of which his son Lothair received the northern part (between Friesland and the Jura mountains), the area which later became known as "Lotharingia" (Lorraine).