FOREST OF (the Sytle Arduenna of the Romans), an extensive woody and mountainous district in the north of France, stretching also into Belgium and the Grand Duchy of the Lower Rhine. It extends westward to the sources of the Somme, Oise, Sambre, and Scheldt, and eastward to the valley of the Moselle. In Caesar's time it extended to the Rhine. Its average elevation is about 1700 feet; some of its peaks attain a height of 2500.