Thionville (tyôNvēlˈ) [key], Ger. Diedenhofen, town (1990 pop. 40,835), Moselle dept., NE France, in Lorraine. It is a center for metallurgical and chemical industries. The town was a favorite of Charlemagne. In the testament of Thionville (806) Charlemagne divided his kingdom among his sons. After being captured by the Prussians in 1870, the town remained German until 1919.