I don't really know much about this subject, but, here goes. Common sense would leave us to believe that, if anything, the Germans would learn from their own experiences and therefore not build a fortified line that would just defend a segment of the Eastern front, as the French did with the Maginot line. So, therefore, wouldn't the Germans build a concentrated string of fortresses to the East of Berlin?

Interesting subject- would like to find out more.

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"The death of one man is a tragedy; The death of millions is a statistic" -Joseph Stalin