10:21 May 17 

this was also one of the first things I had thought of, perhaps something like "physical evolution"?

16:57 May 16 

A couple of points: The Berlin Wall went through 4 incarnations between 1961 and 1975, starting as a wire fence, and finishing as the wall we are all familiar with. Even as late as 1988-89, parts of the wall were still wire fence. Furthermore, there was the 100m no mans' land, with tank barriers, bunkers and watchtowers. The wall itself was 155km. It consisted of many layers, both chronologically, and geographically, but not really anything underground (except maybe parts of the 20 or so bunkers), except in places around the canals, where beds of nails and barbed-wire were installed. I think you might want to consider the historical layers. Words like "extensive" and "complex" may have more to do with this than "deep". Numerous articles refer to gestaffelte Bauweise having to do with the layers of buildings or structures added with successive generations...

11:23 May 16 

could you rewrite the sentence a little and say something like the 155km long Berlin Wall with its complex series of deep fortifications.

10:34 May 16 

sounds like a good place start

10:09 May 16 

I imagine that it is referring to the depth of the wall construction/complex and saying that it was multi-layered, and that the 'layers' varied, I presume. Though how to put that into sophisticated EN, I have no idea.