Reichsfürst
The Duchy of Thuringia was an eastern frontier march of the Merovingian kingdom of Austrasia, established about 631 by King Dagobert I after his troops had been defeated by the forces of the Slavic confederation of Samo at the Battle of Wogastisburg. It was recreated in the Carolingian Empire and its dukes appointed by the king until it was absorbed by the Saxon dukes in 908. From about 1111/12 the territory was ruled by the Landgraves of Thuringia as Princes of the Holy Roman Empire.