The source of the Semois is inArlon,Wallonia, in the Belgianprovince of Luxembourg, close to the border with theGrand Duchy of Luxembourg. Flowing in a roughly westerly direction, it enters France after passing through the Belgian village ofBohan-sur-Semois and forms about 2 kilometres (1.2 mi) of theBelgian–French border.[2] It joins the Meuse 24 kilometres (15 mi) further downstream inMonthermé.[3] The total length of the river is 210 kilometres (130 mi).
The earliest documentation of the name, asSESMARA, is dated from the 2nd century AD. That was before that region was influenced by significant Germanic immigration. Medieval forms includeSesomirs (664),Sesmarus (950),Sesmoys (1104), andSemoir (1244).
The river has given its name to a variety of tobacco grown in the area.[1]