Duke of Alsace

The Duchy of Alsace (Latin: Ducatus Alsacensi, Ducatum Elisatium) was a large political subdivision of the Frankish Empire during the last century and a half of Merovingian rule. It corresponded to the territory of Alsace and was carved out of southern Austrasia in the last decade of the reign of Dagobert I, probably to stabilise the southern reaches of Austrasia against Alemannia and Burgundy. By the late Middle Ages, the region was considered part of Swabia.

The term "Alsace" derives from the Germanic ali-land-sat-ja, meaning "one who sits in another land." Alsace was Alemanni territory, but not so much as Alemannia proper, which was east of the Rhine: it was, however, the "other" land in which some Alemanni had settled. In the late Roman Empire, a district of Alsace (pagus Alsatiae) had been established in the region. Under Chlothar II, Alsace and Alemannia were granted their own law, the Pactus Alamannorum.

In 596, Childebert II bequeathed Alsace to his son Theuderic II, who was raised there. This attached it to Burgundy, but in 610 Theudebert II, Theuderic's brother of Austrasia, forced Alsace' cession to him only to lose it two years later to Burgundy again. In 623, when Chlothar II granted Austrasia to Dagobert, he excluded Alsace, the Vosges, and the Ardennes, but was shortly after forced to concede it to Dagobert by the Austrasian nobility. Sometime probably between 629 and 631 Dagobert granted it as a dukedom to Gundoin, a Frank from the Austrasian heartland of the Meuse valley, a move which tied Alsace more closely to the Austrasian court. Gundoin's duchy comprised both sides of the Vosges, the Burgundian Gate, and the Transjura; there were to be continuous early problems retaining the faithfulness of the Sundgau.

...
Wikipedia