The Hercynian Forest was an ancient and dense forest that stretched across Western Central Europe, from Northeastern France to the Carpathian Mountains, including most of Southern Germany, though its boundaries are a matter of debate. It formed the northern boundary of that part of Europe known to writers of Antiquity. The ancient sources are equivocal about how far east it extended. Many agree that the Black Forest, which extended east from the Rhine valley, formed the western side of the Hercynian, except, for example, Lucius of Tongeren. According to him, it included many massifs west of the Rhine.
Across the Rhine to the west extended the Silva Carbonaria, the forest of the Ardennes and the forest of the Vosges. All these old-growth forests of antiquity represented the original post-glacial temperate broadleaf forest ecosystem of Europe.