Probably just ignorance, but there actually was a gap in that time in some areas in germany. Close to my hometown are the remains of an old ancient fortress - that was build by mostly unknown people and abandoned at 400 b.c. and only 1000 years later there were settlements again. A bit rougher area, though.
The flat area of Berlin on the other hand, had human settlement since 60 000 years.
I don't think anyone requires every hectare to have been developed in order to consider an area inhabited. Neanderthals are named after the Neander valley (Thal) near Dusseldorf, so I think we can definitely say yes, that humans have lived in Germany since long before antiquity.
The flat area of Berlin on the other hand, had human settlement since 60 000 years.